Even for fun bands I've done the learning is at home, rehearsal is for rehearsal approach.
Ok, that's all a bit different with originals as until the song is finished every sessions is a bit of a re-write / re-arrangement but these days with free DAWS and smart phones riffs can be recorded and emailed round in minutes. When I started I had my dad's old dictaphone for riffs and then later a Yamaha MT50 4 track tape recorder!
So I'm very much on the side of turning up prepared to rehearse, having already learned the song at home.