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.
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.