Music allows a group of individuals to honestly and effectively signal to others that they are a coalition, and not just an uncoordinated bunch of losers. By putting on an impressive display of music and dance, one group can signal to the other that they are an effective coalition. The only way could have learned the same songs and dances is if they have been cooperating for some non-trivial amount of time. Don Symons pointed out that applause is specifically not synchronized. If it does become synchronized, then at that point the audience has joined in the performance and becomes part of the coalition.
Rock bands are little coalitions that groupies and fans want to join.
Rock musicians really play up the coalitional nature of performance, exaggerating the synchrony of their guitar playing, etc. A new coalition would only be able to have everybody sing the same thing. Only an older, more reliable coalition would be able to pull off the more sophisticated musical and dance forms. Music and dance are compact, efficient data structures for signaling coalitional status to other coalitions. There may be intracoalitional functions as well.