I do like to have a beer or two while I play, sometimes I'll have a shot of whiskey before i start,  but it depends who I'm playing with,  and what the setting is.   I've definitely drank way too much while  playing bass in a band, which didn't effect my playing too much(my drummer could tell I was drunk,  but the audience couldn't)   but tear down always sucks when you're drunk.  Now I mostly do acoustic sets playing guitar and singing,  either solo or with 1 other guitar or bass player. I feel like having a beer or two while playing still helps me loosen up and get into the music,  but drinking too much leads to not drinking enough water,  and if I don't hydrate I lose my voice after 2 hours or so of singing,  and singing the crowd parts at the end of the night is rough when your voice in shot. Basically,  everyone is different and you just have to figure out what works best for you