Why do keyboards have that one weird key anyway?

So I was typing away on my keyboard today when I realized I have no clue what the Scroll Lock key actually does. I mean, who even uses that anymore? It’s like a relic from the past just sitting there, mocking us while we try to figure out shortcuts and hotkeys.

Back in the day, I guess it had some purpose in controlling scrolling in spreadsheets or something, but nowadays it’s just a strange extra button that no one really touches. Has anyone ever found a cool use for it, or is it just a keyboard decoration at this point?

What’s the weirdest or most useless key you've encountered on your keyboard?