Keavin stated being [intoxicated] on stage is part of being a Musician!. Of course Keavin was not making a statement of fact but merely relating his own personal experience. I'm guessing Yoyo Ma isn't doing qualudes.
Bill quoted Grace Slick, and both, I believe, were probably speaking to the fact that most people are constricted by an illusory view of the world that their Self has programmed through habits of thought over a lifetime of experiences in order to survive in the world, and that feeding your head can provide one with an alternative interface with one's environment that the Self might otherwise be unable to see.
Personally, I have found that a daily meditation practice also provides that alternative interface, and I have found that meditation before going onstage enhances one's ability to be in the zone where the music is the totality of experience and there is no separation between you and your instrument, you and the other players , or you and the audience. It's like the best of all worlds; totally relaxed, totally into the music, the people, the atmosphere; and no hangover in the morning!