Creation of music, seeing people happy, the social thing within the band is the three most positive things about playing live to me.
The put-offs are just as easy: drunken, rude people, being away from loved ones and lugging gear...
And depending on how the venue treats you, that can be positive or negative experience as well.
Actually I find the audience to be a two edged sword, they can be the reason I like to play live and the reason I just want to get the hell out of the whole scene.
I play in a pubband, so plenty of drunken people in those places....