It's probably unfair for anyone to get in trouble over the use/misuse of these because it's impossible to know what anyone else's triggers are.
Like said, it's just a courtesy. If someone posts something they are not aware is triggery for someone else - that someone can politely be like "hey can you put that in a tw I don't really like to see that kind of stuff." If so then I would expect the poster to hopefully not be a dick about it and maybe try to keep it in mind for next time?
Anyways, I don't really foresee it being used too much. Mainly because I think so far we have a pretty resiliant memberbase when it comes to this sort of thing. Once again it really doesn't hurt tho.