But that's not an excuse for not working at your part at home
Do you know how many rehearsals Dream Theater had with Mike Mangini, before hitting the first tour together? ONE rehearsal out of what I have heard
Maybe that's exaggerated, but when you join a band, you most certainly don't learn the songs in the rehearsal room. When you write music together, a good idea is sparked at the rehearsal room and then pre-production kicks in at home on the computer. That's where the idea starts to shine. It's like digging a out a diamond - you know it's valuable but it won't shine until a jeweler will give it its facets
This is my approach.
That's what I call being professional!
I think that as Marcus said, everybody must go to the rehearsal with the parts learnt and well played so one rehearsal could be enough if each member does his homework.
I like practicing in front of the computer and use drum loops, songs and metronome to do it. GMC backing tracks are also one of the things that I mostly use for practicing.