Starcraft-2: When to wall in?

When and when not should i wall in?

In some replays i've watched casted by Day[9], he says things like "Oh i generally wouldn't wall in here" etc etc. However, my understanding of what type of situation 'here' is is quite poor. So while i was under the impression walling in my main was a sound strategy, the experts suggest otherwise.

So, to be thorough, what are the benefits/drawbacks to wall in, and for what match-ups?

Solution 1:

The link contains extensive information about walling including: definitions, competitive use vs the various races, building/unit placement and the associated disadvantages. I hope this is useful and apologize again if i am doing something wrong here but I'm kind of new to this forum.

http://wiki.teamliquid.net/starcraft2/Walling

Playing AS - AGAINST

TvZ - Walling against Zerg is common to prevent zergling run bys thus preventing scouting and harassment of your mineral line.

TvP - Against Protoss you can wall off early if you are expecting a zealot rush from a proxy gateway or a 4gate rush build.

Generally as Terran walling is effective because you can use supply depots and liftable buildings to create a gate that you can control rather than a wall.

PvZ - Same as TvZ you want to wall in to prevent run bys. The difference here is that you want to leave youself a gap (1 unit wide) to allow your units to leave the base later. You need this gap because you cant move your buildings once they are planted. A zealot is a very effective plug for this gap as zealots are vastly superior to zerglings 1v1 and the zerglings will be unable to get a surround.

PvT - I refrain from walling as Protoss against Terran because I find that it just places my buildings in front of my attacking units thus enabling the Terrans to abuse the range advantage at the early stages of the game. It seems more important to have my buildings near my mineral line to prevent drops and lower the distance defending units have to travel to respond to threats.

Zv Any - walling in with buildings is nearly impossible (at least impractical) at the early stages of the game. Later high health units like roaches can be placed at the tops of ramps or in chokes to limit the enemy movement through these already small areas.

Solution 2:

If you're going up against Zerg as Terran or Protoss, some form of a wall is advisable to prevent Zerglings running clear by your main choke and harassing workers. Terran can just use buildings, Protoss should make a 1-2 wide channel and have a Zealot hold position in it

Solution 3:

I almost exclusively wall-in versus zergs. The 24 lings/banelings push is very hard to stop once they're inside your base by trivial matter if they can't get in.

Also, in maps where the natural expansion is very close to the main, I sometime wall-in below the ramp so I can protect my fast expansion more easily.

The downside to wall-in is air. When your units spawn far from your minerals, your workers become more difficult to protect against mutas and voids and medivacs. While the rushes are an all-in strategy (player failing a rush is most likely to lose) and thus, not favored by higher level players, air attacks are almost inevitable, or at least, a serious possibility in virtualy every game