I know you have them. I have them too. Everybody has a plethora of orphan keys stashed in various places around their houses. These are one of the hardest things to get rid of.
See, if you don't know what lock a key belongs to, chances are you don't need the key. But IF there comes a time when you realize that you need that key? You really need that key. Or you need a hundred bucks to give to a locksmith.
It takes guts to throw away spare keys. Even (especially?) if they're weird little ones.
This key has lived in a bowl on my desk for years. I'm nutting up and throwing it away.