This wall is impassable for Zerglings/Marines/Zealots/Drones
This wall is impassable for Zealots/Probes
Use the Overlord trick (select larvae together with an Overlord, press stop, wait for larvae to go left, and hatch a unit) to make this wall even better
Dragons can't get through this wall, we recommend destroying the blocking pylon or gateway later in the game
Use your micro and simcity to fend off the Zealots! The gap between barracks and supply is passable for Marines but not for Zealots
Building a gas extractor makes the gap passable
Korean progamers build cannons differently based on the position they are spawned. Some of the positions don't allow for many cannons to be placed,
while it's crucial when defending against the 3 hatch hydra build.
Building them up against a wall makes them easier to be sniped by range less hydras, but building them one hex off is harder for building many cannons and making the way passable by units. Putting them one back also helps against small numbers of zerglings. If they get past and try to run up the ramp, they can sometimes cover more area. However, if it is a large number of lings, they are easier to surround.