Inspired by Babytoss’s posting frenzy I have wanted to write about why you scout. The reason why this question comes up is due to the discussion on whether the liquipedia is right when it suggests that 13 supply is the correct timing to start the cybernetics core or whether 14 supply is more optimal? The answer basically boils down to when you scout.
(Note that this posting assumes maps like Neo Medusa or Longinus).
If you scout at 8 supply (right after your first pylon), then you can’t afford the cybernetics core before 14 supply, but if you delay the scout to after you start the core, then you can afford it at 13 already.
So what are the pros and cons of scouting early?
If your opening is risky and have to adapt to whatever your opponent does, then you should scout early. If not, then your early game economy and the speed of your build is increased a lot, the more you delay.
The risk of the 10/15 gate opening against Terrans is mainly if they decide to cheese you by building proxy barracks. That is a real risk, but I have never once seen that done on the level where I play. So by scouting early you could see the cheese and decide that your first unit out should be a zealot and not a dragoon. Since zealots builds faster, that might give you a combat unit out slightly faster to defend against marines in your base.
Scouting earlier would also allow you to get inside his base before his wall-in is completed. When you do that you could potentially figure out whether he intended to fast expand or go double factories. Unfortunately your probe have to survive being chased by marines for awhile before you can figure that out. And to make matters worse, some of the signs are not reliable on my level of play.
For instance Terrans rarely takes SCVs of gas even though they are fast expanding, so you can’t really deduct that 3 SCVs on gas means a double factory. So usually my probe ends up dead before it figures anything out. And it was not that I cared that much anyway. My first 4-5 dragoons + 2 dark templars are both useful for delaying a fast expand and to stop a two factory push.
Basically my conclusion is that I don’t see the point in a very early scout. It delays my first dragoons, risk the scout getting killed and will rarely yield any information that I wouldn’t get equally well when scouting earlier.