Went through and deleted a bunch of PDFs off of my HDD that were of RPG systems and settings that I have no intention of playing or reading. Part of the criteria was the following:
1) Does it have a non-open license? If so then it's more likely to get chucked.
2) Was it released by someone who later turned out to be an asshat? If so then it gets chucked.
3) Is it a classic game? If so then there's a higher chance of it sticking around.
4) Is it by someone that I admire? If so then it stays.