It's a risky move only because people don't
practice doing it!
Everybody has experience with a Marine Start base, but not many commanders can actively select a new base location on the fly and have a team competent enough to work together and actually aim.
A creative, strategically well placed relocated base can have huge pay offs. Often time I see games where were alien stacked and the relocation alone made it a much more balanced and longer lasting battle, not to mention more interesting. In public play a relocation it a psychological break in the ususal monotony of a MS base and actually makes your average player work more with the team. And perhaps most important: a good relocation that locks down a chokepoint or hive can really screw aliens over throughout the game. Just be aware that beacon will NOT take you to your base without a PG in Marine Start and a PG in your relocated base.
Tips for relocation:
- Recycle your Marine Start command chair, you can kill yourself one the first IP is built and have a teammate do this recycle
- Don't waste resources until you have your new base going
- If on a large server, you can have some small squads serve as distractions or resource grabbers en route to the relocation
- Results are best if you can have an area you can control and easily access multiple resource tower nodes and or hive
- Try to build in a choke point, but don't forget to use mines and/or turrets to keep away skulks and lerks.
- Avoid the high traffic areas of the alien team, drop base where they are not. This is important!
- Avoid an area that's too far out of the way to grab RTs, this is why relocating into some hives can be a poor choice
- Not as important, but if you can avoid places where you are in the far back of a room with only one walkable entrance (don't count vents)
- Can serve as a backup plan to an early game hive rush, as long as you have enough resources
- Don't leave your base undefended forever, alien teams generally seem to do a better job at trying to rush your base together instead of one at a time in games with marine relocations
- Try having a "base monkey", some guy who listens well and guards your base and PG's while building stuff so the rest of your team can be always on the offensive
Here's some examples:
Map: ns_altairStation Monitoring Main -- MS is actually very poor for defense since it is so open and long. This relocation may be hard but is highly rewarding when used on large public servers where your marines fan out in large numbers from the central area of the map. Both Omega and Consistency Hive locations are fairly close but more importantly this is an easy to defend base location when you set it up like this and thus easy too resist that early base rush any alien team with a few competent players is going to try. And when you repel that attack you have easy access to numerous RTs in Station Monitoring Power, Station Monitoring Annex, Sub Bay, and with a little more walking or a mine step-ladder, Consistency Hive RT. Like in chess, control the center of the board for the game and you'll win most of the time.
Map: ns_ayumiNorth-West Turn -- in the area between Pressure Control Hive and Information Bank to be specific. You grab the Server Outlet RT on the way, then the seond one and drop the comm chair next to it. You drop IPs also next to the RT and eventually electrify the RT for an effective defense. You can easily keep seige control over the hive area, hold two resources nodes and have easy access to Cold Turn RT and Hamaski Hive and RT. Then build a PG link between cold turn and your base. Beacon at some point and grab back MS and powerbuild a PG link there too. If you are successful you will have control over a hive and at least 2-3 RTs. Examine the pictures below.
Map: ns_eclipseT-Junction -- drop the RT and build your base in that long hallway, It gives you seige control over South Loop and easy access to both Maintenance and Computer Core. However do not choose this relocation if their hive is Maintenance, or several skulks are going to Horseshoe to cut you off. If they have maintance, SAA or Triad are great relocation spots too. And by Triad I mean up on the high-ground looking down at the Triad RT, NOT down in the "pit". It's hard to defend against lerks and fades down in there.
Map: ns_nothing#1
Generator -- a well known choke point and gives you great access as well has the high ground on the north entrance. It's a medium sized room with a special balcony you can build a mine ladder up to, only two entrances and give you a RT as well as seige control over two other RTs. I've won several games by relocation to this area. To achive victory, try to lock down the two RTs by Cargo Hive for resources and hive control, but to do all this you
MUST HOLD the chokepoint which is between these four areas: Quad Lift, Intimidation, Miasma, and Painted Corridor. Look on you map and you see the area I'm talking about, it's by that vent which run from MS. If you lock that down with troops, turrets, mines, or any or all of those you will crush their team. It is not easy, but it is fun for both teams actually albeit a bit frustrating for the alien team leadership.
#2
Between Cargo Hive and Ventilation -- You can control a hive and two RTs obviously, but it can be hard to move out. I didn't rate this one as high because it takes phase tech early on, hand grenades preferably, and a marine team that actually listens and moves together to win.
Map: ns_tanithCargo outside Fusion Hive -- It's really hard to get a base started in there, but IF you can it's hard to loose. You not only control 2 RTs, a Hive, and a critical chokepoint, but you also have easy access to the Chemical & Acid "Double" RTs, and the the more well-known Reactor Room which is what is usually refered to as "Double".
Chemical Transport -- Controls access to Sat Comm Hive, 2 RTs (acidic being the other) and has easy access to both Cargo and vent access to Reactor Room. This is an
EASY place to relocate to if their hive is Waste. Try it sometime in an actual game, just make sure you have you mic on to communicate to your team.
Reactor Room -- If it wasn't as hard to defend it'd actually make a better base, but of course the more RTs the better and there you have two within plain sight of one another. I do suggest welding weldables shut ASAP. (and a welder only costs 5 res an a little labor-time of welding) The problem is that most teams go every-which-way when the base is double and aliens love to cap the rest of the map when marines are there. You also only have one choice, you must lockdown the Storage Entrance choke point.
Map: ns_veil#1
Between C-12 and Pipeline Hive -- If they have Sub-Sector tell your ENTIRE team to rush southeast. Have one marine hold back to grab RTs on the way but the rest must NOT stop. Lock this area down. The sack cargo from dome or screw the gorges in double. Moving fast in large numbers is key. It's easy to move out fast on the eastern side of this map. Research cat packs first! Unless they have SC, just get weapons upgrades fast. If they are packing SC, get MT and armor upgrades, up to HA. But as far as strategy... Try to nail Cargo Hive from dome while denying double, this is the breaking point. Once you control Cargo Hive, equip HA with weapons as best you can (no HA, just drop weapons, a few mines and welders too) and beacon when you have the aliens mostly on the western side of the map. Do a southwest HA train rush to the hive. This is highly effective at this point because your team just did this same kind of manuver at the beginning of the game, but now they have big guns and armor while aliens are already worried. I usually see aliens take the beacon as a cue to abandon Sub-Sector and grab double, move towards your base, and/or Cargo. This is a bad idea. They want a hive bad, and actually often will drop one but your cat pack powered HA train will plow down the western side of the map and smash their hive location. Once it's down you just mop up the survivors in a brutal fashion. You can put your base either in C-12 or Power as the screen shot below signifies.

Note: You have an easy 90 degree coverage of all the key structures, AA in center with hidden mines, PG could be anywhere near IPs really. But the placement of the structures in the window and AA in the middle is key to an easy defense.
#2
Sub-sector Hive -- it may at first seem out of the way, but it's extremely defendable. If you prefer a more defensive style this is your ideal base. You can't be all defense or you'll loose, so make this a launching platform for assaults. Work a western control to outer rim control pattern. Ignore double except to deny the aliens it if you get the opportunity. That means grab Overlook, West, MS, Topo, and as far around as you can get before aliens rape that RT capping squad. Then rush for a Prototype Lab and get either HA or JP. There are so many factors for that decision. But your next step after you get HA or JP is to push the fades back with HMGs then get a marine who is really good with the GL to be artillery. The rest of the team MUST protect the artillery. Assault a hive. Attack cargo or ninja pipeline.

Note: See how the base is built in symmetrical levels of lines of defense? What you can't see are the clever mines protecting the AA and IPs. Electrification is ideal and very useful, but do what you can with what you got.
#3
Overlook -- An easy way to hold an RT and deny a hive location while giving access to double. If you are one of those commanders who loves double and for some reason feels the need to keep capping it on this map consider relocation here. Get a PG link up between double and here for success. Work a western & central control of the map. Ninja action will be key. Just keep on your toes, a smart alien team will pick your RTs off with bile bomb as soon as they can.

Note: See the mines by the vent? That's critical to good defense. It's also easy to do with no boosting needed, just aim.
PS for ns_veil: Double usually sucks as a relocation against anything but bots. Sorry, but it's true. Don't let greed for resources fool you. It's easy for everybody to get to double. You'll simply be outnumbered and mauled by a competent alien team (ie: lerk gas and/or fades), plus you can seige it from the west or east at any time, you just have to act fast. It's easy to deny, nearly impossible to hold. If you want double, weld the vents shut first.
There are many, many others and I have a lot of experience with them. Just tell me a NS map and I'll give you it's best relocation spots with as much detail in tips as you want.