If the festival has multiple stages competing for the audience's attention, it is less likely that many spectators would attend each of a given performer's shows. In such cases (like the New Orleans Jazz & Heritage Festival, coming right up this coming weekend and the next), it makes sense to include a fair amount of "overlap" ~ maybe 40-50% of each set consisting of repeated material, the artist's most popular numbers.

Where there are fewer stages and more appearances per performer, it is more important that each appearance be "fresh" and different, because most if not all of the audience is likely to be the same for each show.

Repeating songs/tunes is one thing, of course, but repeating banter and jokes ~ especially verbatim! ~ is ten times worse. Liz the Squak's story tells us why: the performer makes an immediate bad impression on anyone and everyone in the crowd who's hearing the stuff for the second (or more) time, leaving a bad taste that potentially outweighs any favorable reaction the folks might have had to the essential part of the performance, the music iteself!