On longer feature pieces there is almost no such thing as enough. The key is still variety. Make sure you tell your story. You often have to lead them along because often they get distracted by the pretty lights and shiny objects but stay focused. One of the most important thing is the post game analysis.
Second chances are as rare as spontaneous pay raises.
What I try to do is talk over the story with the reporter and put it together in my head, then shoot what I think I need, a few safety shots and away we go. Often, I'll get the surprise shot that was unplanned but makes the story, you can't count on these, so I consider them a bonus. The way I see it, your done when your done. Funny though, it always seemed that I always had all this great stuff that never seemed to make air, and editing was a bit of a chore because I was shuttling and winding A LOT of tape. If you only need about 5 shots, you don't need to shoot 50.