You have to decide what your objective for each rehearsal is--this is a bit trickier than it seems, because it means that you have to all agree on where you're going and how you're going to get there--

Some like to play loose--get the bare bones worked out, then wing it for performance. Others like to be letter perfect before they take something out to play. There tend to be some of each in most bands, but if you agree on which way you're going to do which songs ahead of time, often, things can be worked out.