Yeah, I often am (happily) clueless as to a lot of the bands I'm working with until they walk on stage and play. Though I can tell a lot based on the people waiting to go in and see them, and what I am setting up for them. Four (count 'em) four sets of inputs for ProTools? Yeesh, why tour, just send the computer ahead to play.
But I've had to suffer though people I like, doing music I thought (until that moment) I liked, and also watched people I didn't much care for turn in great sets - so I never know.