Linux & BSD can make them useful as servers, media centres, retro emulators or even a desktop pc if you are patient.
They will chew more power than a raspberry pi but they are easier to come by.
An old desktop and an old laptop is enough to get a solid selfhosted homelab and media centre up and running.
Current favorite suggestion is install linux, navidrome & tailscale on an old machine with your music library. Then connect with Symfonium, web client or other app and enjoy.