I'm watching Huk atm, and it seems that in the really early game (where your doing nothing but making a worker and watching it train), he is constantly selecting his probes then selecting his probes, rinse repeat, rinse repeat, etc. Why? Is that to get his APM's up or is there actually something there I'm missing?
It's sort of a warm-up practice among higher skilled players. The idea is if you keep your fingers and mouse moving quickly at the start of the game, then it will be easier to keep them moving quickly when you really need to later on. Getting 300+ APM is just a nice side-effect.