Big Game Hunters/Wall-Ins
Terran Wall-Ins are super important on BGH for Terrans who are going tech (and it can make it a bit safer to go MM, too), because it's a map where action starts really soon, so you must be able to stop the initial rush. The fact that it's still surprising, is that BGH players that have been playing BGH for a long time still don't know how to properly do a Wall-In on all positions. The Wall-Ins posted on a screenshot below are all lingproof. What's important to note is that the 3, 5, 6, and 7 Wall-Ins spawn Marines inside the wall. The other Wall-Ins do not. Yes, the biggest problem is with the Wall at the 3 where most people still don't know how to do it so your Marine spawns inside the Wall, which is actually a pretty big thing.
Click for larger image
There is a trick Protoss players can use if the Terran is using a vespene geyser as part of his wall. Since vespene geyser's have a larger collision boundary than do protoss assimilators, a protoss player can build an assimilator on the geyser to allow units to walk through. This can work at the 6 main to allow zerglings to run through, but at other places the gap can be made large enough for zealots to pass as well. It is something to take into consideration when using a geyser as part of your wall.