Is it acceptable to lock a child in their room?

I’ve actually known multiple people that lock their child in their room for nap time/bed time/as a punishment. Most recently I saw a video posted from a former colleague of mine. She has a 2.5 year old. In the video she says “let’s see what XXXX is doing instead of napping” and she walks to the little girl’s room and it focuses on the door knob which you can see is turned around to have the lock on the outside. She unlocks the door and it’s a pitch black room. She flips on the light and the little girl is sitting up in her bed with books and toys. I knew another person who would lock her kids in their room if they were crying/whining/acting up and sometimes leave them in there all night, she’d just watch them on a baby monitor. Do you think it’s ever appropriate to lock a child in a room? I personally find it cruel and dangerous. What if there’s a fire? What if you’re incapacitated and the child cannot get out?