I always scavenge any electronics I'm throwing out, even if I only have a limited amount of time. For a long time I’ve considered empty computer cases to be worthless, but there are a few things that are worth keeping. Excluding the power supply, most of the parts are on the front cover.
The LED’s and buttons aren’t worth a whole lot, but they come with pre-soldered with a short jumper cable that's ready to be plugged into a header somewhere, there time savers.
There’s also the fan and maybe a few stray cables. If you also tossing the motherboard there’s a treasure trove of random stuff, but no matter what I always take the coin battery, it takes 3 seconds and it’s nice to have a few spares.
If your case has front USB and/or audio the board those are housed on generally pop of with one or two screws, and they already have a nice cord and terminators, just like the front buttons.
Most of the stuff is pretty handy, things that are nice to have on hand if you ever have any electronics or robotics projects.