Didn't like and didn't know are completely different...
I've stayed for a few Godsmack songs to see how they sound live (Rob Zombie...opened!?) ... Didn't like 'em and we left a few songs in and beat traffic.
Went to see Bang Tango, but stayed for House of Lords, who I was unfamiliar with. If we hated the first couple songs, we would leave. However, I ended up loving them, so It was def worth staying.
I know different people have different responsibilities and schedules or what have you, but I enjoy getting what I feel is my money's worth.