I have pretty much the same categories that Ian describes. When I'm photographing birds, for instance, random factors like subject movement, wind, quickly changing light, and such necessitate making many exposures, because you can't tell when you've got it, even when you're fairly sure you've got it in the field, until you edit. If I've got three great shots and maybe 10 usable ones for certain circumstances and 15 others that are wrong for some reason or other, all of the same bird from the same setup, I toss the 15 that failed. They just clog the files and become a storage problem.
I once lost many of my early negs to a basement flood. I was away at school, and my parents had moved to a new house and didn't realize they had a flooding problem. When I came back, I went through all the pages to see what could be cleaned and salvaged and what was important, and I made some choices, and although I would have rather not have been forced to make some of those choices because some negs were unsalvageable, I thought it was a good exercise in the end. I had enough distance from them at that point to know what would be interesting later on, and I have gone back and printed some of those images.
Now the main issue is Manhattan real estate. If you live in a house in the suburbs, sure, go ahead, save everything (though I still think there are advantages to editing, even if you have room for all the negatives you ever make). If one lives in Manhattan or central London or another expensive high-density city, it really is necessary to think about every square foot. Just to give an example, I own a classic Gibson L-50 archtop guitar that I bought with the original case. The original case makes the guitar more valuable to collectors, but Gibson used the same case for everything in those days even if it didn't fit particularly well, and I bought it to play and needed a practical case that would protect the instrument, and I couldn't afford to be a collector of bulky guitar cases, so I had no problem selling off the case to a collector, even if it was worth more with the guitar should I decide to sell it in the future, because the difference in price is far less than the cost for even one month of owning or renting a larger apartment.
I once lost many of my early negs to a basement flood. I was away at school, and my parents had moved to a new house and didn't realize they had a flooding problem. When I came back, I went through all the pages to see what could be cleaned and salvaged and what was important, and I made some choices, and although I would have rather not have been forced to make some of those choices because some negs were unsalvageable, I thought it was a good exercise in the end. I had enough distance from them at that point to know what would be interesting later on, and I have gone back and printed some of those images.
Now the main issue is Manhattan real estate. If you live in a house in the suburbs, sure, go ahead, save everything (though I still think there are advantages to editing, even if you have room for all the negatives you ever make). If one lives in Manhattan or central London or another expensive high-density city, it really is necessary to think about every square foot. Just to give an example, I own a classic Gibson L-50 archtop guitar that I bought with the original case. The original case makes the guitar more valuable to collectors, but Gibson used the same case for everything in those days even if it didn't fit particularly well, and I bought it to play and needed a practical case that would protect the instrument, and I couldn't afford to be a collector of bulky guitar cases, so I had no problem selling off the case to a collector, even if it was worth more with the guitar should I decide to sell it in the future, because the difference in price is far less than the cost for even one month of owning or renting a larger apartment.