These weren't my keys, thankfully (or unfortunately, for those whose keys they were), but it was still a waste of whatever time it took me to get there, do part of the dungeon and leave with nothing.
These were all "we've wiped, dungeon is done!" bails from petulant players, but my play time is extremely limited, so when I do have an hour to run a dungeon or two, even having one bailed can affect my ability to get anything meaningful done that session.