About 2 years ago I was pedaling up a rather steep hill and missed a shift into “granny gear”. I couldn’t unclip in time and toppled to the right in slow motion, helmeted head first into a guardrail. I saw stars and was a bit befuddled for about 20 minutes. Without the helmet I’m pretty sure the mild concussion would have been a lot worse, not to mention the possible bruises and/or lacerations.
In any case, after about 60 years of mostly helmeted riding it was the first time I benefited from it. Still, I think it made all the prior helmet wearing worth it.