veinbuster
Zombie Three, DFZ
I agree that time playing together makes things crisper. Few bands these days play as much as we did. 3-5 nights a week for 3-4 hours is enough to bond pretty well without adding rehearsals. Good odds we would play 150-200 songs before leaving town.I have been in the situation you describe as well. It usually happens at jams. I have played songs at jams that I have never learned but I have heard them enough that once I knew that key to play in I was able to keep up.
To me, there is a difference in how tight the band sounds when things are rehearsed. It doesn't take many hours of rehearsal if everyone is prepared. I know I can hear a difference in the bands in my area that rehearse and those that don't. However, that is not to say that if people do their homework that you couldn't play the song as a band at a gig for the first time. That all depends on how well you all learn and how well you play off of each other. I have been in that situation as well. It is nice when you are in a group that can do this. You just learn it at home and add it to the list.
When I got back to town after being away for about a year, we did ‘rehearse’ by doing a set at an open mic night at a local bar a couple of days before hitting the road.