When I was shooting film for everything I almost never got rid of any negatives. A combination of both irrational reasons as well as rational reasons combined to make me keep everything I shot. From a rational point of view if I was shooting roll film It was more trouble to cut individual negatives out of the strip rather than just filing the whole thing. For sheet film if there were technical faults or aesthetic faults I would make notes on what went wrong for educational purposes - mine mostly.
As time wore on and I made it a practice of reviewing contact sheets of things that I had shot years previously a few things occurred to me over and over again. The first thing was that a lot of the "faults" are not more than a passing stylistic fancy that you happen to have at a certain point in time. Second, other more technical faults are either irrelevant for a particular image or are so secondary to the image that you don't really care about them down the road. Third, images that you may have decided are superior for inane reasons, like they are sharper or have no subject motion, are not nearly as good as the one right next to it that happens to have a little subject motion. This can be true of any image I guess but I have found it especially true of people.
Case in point. When I first shot the images included with this post of my 3 year old daughter I knew that they were not going to be great due to the fact that I grabbed my camera that was loaded withKodak Plus-X film and just started shooting. Plus-X is ISO 125 at best and this was an indoor shot of an animated 3 year old. As I fired off a couple of shots I "knew" there was going to be subject movement given that I was shooting at 1/30. I developed the film in PMK Pyro because all of the other exposures on that roll were perfectly exposed for that developer. The first prints that I made did not include these two. In fact they included none of the 5 shots in this series because what I "knew" was true - there was a ton of motion blur.
Years later when I was going through contact sheets I decided to print these two images. Turns out I like them way more than my other perfect images on this roll. Heck I forget where the original prints that I made of "perfect" frames are.
I guess my point here with digital is that I am still an image pack-rat and almost never get rid of images. I get rid of images that I take for e-bay auctions and such but almost never delete anything that has people in them. Especially people that I care about. I know there are two schools of thought on this but given that storage is small and cheap why not keep them?
My advise is to leave the things alone - at least for a couple of years.