Beer enhances many things, it enhances courage, it enhances stupidity, but if there's one thing it doesn't enhance it's performance. Amnesia plays when he's stoned on pot, but I don't think he actually thinks it improves anything either (or at least I hope he doesn't think so).
Sure, beer impairs judgement and coordination, but if a person's playstyle is very much overly cautious -- i.e. they feel the need to double- or even triple-check to make sure a move is okay before making it -- then a few units of alcohol will probably help them to play faster. Alcohol may also help overcome nerves in a competitive situation; I personally find that I perform much better at vs. mode tetris when I've got a couple pints of guinness under my belt
I play keyblox and then it makes my tgm play better. WAT? more seriously, I need to pull my joystick out more often.