I think the written legal waiver was mentioned because it would be the only verifiable evidence to defend yourself against someone claiming such advances were unwarranted.
That's one more reason to make sure they are. If there is ambiguity it is safer to err on the side of caution. Note that anybody that you were in a room with could make up such a story, so you're always going to have to rely on good faith to some extent and false accusations really do happen.
