Back when I went to a lot of Bluegrass festivals, The Dillards were an example of a group that had very good seemingly spontaneous, but well-rehearsed patter and an entertaining show, but you found that if they were booked for two or three days that you'd get to hear the same two sets verbatim three times during the weekend.

The late Joe Val & The New England Bluegrass Boys were an example of the opposite strategy, telling audiences right off, that if they wanted to hear a specific song, either again or if you'd missed it the first time, you'd have to specifically request it, because they prided themselves on never repeating a song during a weekend stand unless specifically asked to, as they felt they owed it to the audience. Maybe "Sparkling Brown Eyes" might get a repeat, but the crowds were fine with their policy and were always rewarded with a good show.

Even bands with an established and expected set of "hits" can manage to alter their presentations during a weekend.

The best acts that have been around long enough to manage to have an extensive repetoire always do well to vary their set during multiple festival appearences.