Earlier quoted context omitted.
On MacOS if you remap your capslock to control there is a race condition on the login screen. If you use the control/capslock key to wake up your laptop and manage to time it right, you can enable capslock but not have a way to disable it (unless you remapped another key to capslock (why?)).
Funny, I just had a version of this happen to me this morning on iPad OS using a folio keyboard. I had just upgraded to iPadOS 15 and the caps-lock-as-control setting reverted to the default. I went into settings and changed it back, but I did so with caps lock accidentially enabled. This left the folio keyboard stuck in caps lock. I had to go back into settings, set caps lock back to caps lock, press the caps lock k…
It was useful on some old machines that tended to prefer uppercase input. On typewriters, the shift lock key (which is slightly different) tended to be used when people wanted to add emphasis to a word or phrase.
As for modern computers, it is less useful. When one of the keyswitches on my keyboard failed, I replaced it with the keyswitch from the capslock since I figured it was the one key I was guaranteed to never use.