Its not just if they want to play more songs, its also if they want to play something different. Its similar to an audible in American football. The QB calls a play in the huddle, the defense sets up a certain way, the QB then changes the play because he thinks it will work better.

Example: At the BJ show I was at in Milwaukee they were set to play Wild in the Streets but Jon ended up switching and playing Blood on Blood instead, which was a good call.

CW