I start worrying at frame #35 when I shoot bulk film, since I never really know how many shots I get before I reach the fogged end.
A few years ago, I "archived" all my old negatives to digital and found that 95+% of my rolls had "wasted shots" at the end, typically images of rooms of my house, a bookshelf, the backyard, etc. Interestingly, some of those "wasted shots" images were among the most interesting images on the roll. How many of us consciously take photos of our homes, rooms, furniture, cars, and so forth? 20 years from now, those photographic images will probably be of more interest than the plethora of awesome sunsets, beautiful flowers, and majestic mountains.