It would affect my performance just WATCHING someone drink a fifth of vodka and try to play!
However, I opened a show for Ray Price once, and two guys had to help him on stage, each holding one arm. I thought he'll never finish the first song, but he did a great show and never missed a note. Then they had to help him off stage. That was 35 years ago. He was no doubt partaking off grass and not booze though.