Only thing that makes me leave is if it is super obvious the group won't be able to handle the place. Even then though I will still wait most times (if someone else leaves) for the group to fill again. Why? It's simple. I. am. dps. The wait times are so ridiculous sometimes it is just faster to wait for another person or two to come in and try to see if they will be effective enough to get us through the place. It drives me crazy though when it seems most people finally got the fight down and one more shot may get the kill, only for some impatient person to just up and leave. If it's the tank, half the time it kills the group altogether.