Someone mentioned macros, I have to say that they seem to be a bit.... superfluous. Most pros for games that I watch don't use them that often, or at least not that many. I know that for WoW some people use them for rotations or just to not have to bind their entire keyboard. I know that I've never used mine.
Well, for those of us that are decidedly
not pro, they're very useful. In fact, I would probably say for that reason that they're so useful. Someone that's already so good that they're a professional at a tournament, I really doubt they would need something like that... some tournaments probably even ban that sort of thing.
If someone is super skilled they can perform very complex micro without breaking a sweat over and over, but normal users will have a hard time pulling it off even once... That's where macros come in and close the gap a bit so that those of us that aren't pro can do a little better.
It may just be for ease of use things too, like just making things easier for ourselves. I mean, I could hit a combination of something like (space down) (w down) (w up) (space up), but assigning it to a macro makes it a lot easier for me. And when you get to something more complex that you have to do super fast like {w down}{+ down}{RButton down}{w up}{+ up}{RButton up}{Space down}{w down}{w up}{space up} (repeat over and over) then that macro becomes incredibly useful. Not just for making certain gameplay things easier, but also to prevent stuff like carpel tunnel.