I used to find it handy to keep a few ancient PCs, a Pentium 4, a P233MMX ... great way to always be "100%" compatible with ancient software (games) and easy to pimp them up with garbage spare parts. At least it uses up a few of the best of those puny old drives. In recent years it seems like cross-platform intercompatibility and emulation has become a trivial non-issue, although no doubt one day I'll need one of these genuine machines to run a piece of dinosaur software.
I turned a few junk HDDs into fans, I found it hard to cut and bend the platters into fan blades without breaking them (although it can be done, and I used up lots of spares) and some of those stepper motors have a lot of max rpm but also make a lot of noise.