NONE
But for the sake of argument lets go down the logical paths
If he goes with his g/f:
He spends the night pushing off guys trying to sandwich his g/f.
Silverlining
If his g/f is the explorative (is that a word? i doubt it) type theres a 12.4 percent chance of a threesome
If he goes w/ out his g/f:
If he doesn't drink, He's probably looking for a ONS or something on the side. I don't know any straight guys that go to the club because they like to dance.
Pick your poison.
Bare in mind i'm refering to dance clubs, if it's a night-time lounge or Jazz Club, those places can be excellent places to network.