I don't drink, but I do partake of another substance that has been rumored to have music enhancing powers. To me, I can handle playing while on that substance, and actually find it much more enjoyable, but I have never let it get in the way of my playing. Nor have I ever been talked to, at or fired for using this unnamed substance. So I think that if you feel you can personally handle it, why not take a couple drinks before you go on? As long as it doesn't alter your playing and/or personality for the negative, I'm all for it. In my experience, however, alcohol and music don't mix very well. But that is my experience only. As for the "other unnamed substance" it is undeniable that some of the best music has been created while on it, and in my experience, some of the best jams I've had were on it.
Plays hell on writing though... Larry Niven wrote about the unnamed substance being the death of creativity in either Playgrounds of the Mind or N-Space, I can't remember which. I do remember thinking when I read it, "YMMV Larry, always YMMV."
I played with a guy who while a chronic user of the unnamed substance, but won't touch it before a show, he starts thinking about pizza, and there goes his playing...
A couple times in my younger guitar playing days I dropped...shall we say Jimi's fave...before a jam session (just guys screwing around, not a band situation) and that apparently turns me into the best metronome for speed metal. At least until the frets start the Dance of Fairy Queen...
I'll usually have a couple or three beers before the show, one or two on stage, whatever after. Usually along with some unnamed substance.
The thing that is death on me for performing is ibuprofen. I can take aspirin or acetaminophen, no problem. Take one ibu and my timing goes right out the window. Funny thing is the drummer has the same problem, one rehearsal we both kind of brain farted and took ibu's before, sure enough both of us were right out the window on our timing, right out the SAME window... Been playing with the guy for more than 20 years now, but I didn't expect that.
Guitar player was distinctly relieved when the drummer and I were loling about it afterwards, I guess the poor guy thought he was the one out to lunch...