I'm glad it's an option, and if I was posting, like, unlocked nude photos or something regularly, I would probably use it, but I think anything I've posted even slightly like that anytime recently has been locked anyway, and there's not much point in the adult content setting for locked content, since anyone seeing your locked content presumably knows what they're in for.

I suspect people assume there's some sort of clickthrough but may not realize exactly how annoying it is.