I once set up a computer workshop using PCs discarded by university labs. I assembled about a dozen PCs from about 20 discards. One of them served as a DSL router.

In retrospect, I regret it; I saved those PCs from going to the dump, but:

- They were not power-efficient

- Because the hardware was a decade old, they had poor connectivity options

I used to seek out computers that were maximally upgradeable. But in practice, the only thing I ever upgraded was disk and memory. I still have a box of obsolete memory cards. Stuff gets obsolete very quickly these days.