I generally save everything I can possibly imagine ever using. Now and then, I get into a purging mood, when I feel like I'm just tripping over shit all the time. My shop is just a fucking disaster right now, with my Guzzi torn down to its elements, woodworking/boatbuilding projects, and the ongoing disaster of living with a 200 year old house. Add to that my 4 and 7 year old kids working on their "projects", and our free-range chickens getting in there and shitting here and there (Oh look, I found an egg!) I've also got a fair bit of crap leftover from an RD350 project.
That said, it is immensely satisfying to have on hand what I need to help a friend, or myself.
I wouldn't bring her home to Mama, but Mama ain't home tonight.