@Classified Ah... no, no, no... you got that all wrong.
It affects who can see your posts - like adult filters to over 18s only, family safe is likely to filter to younger audiences, too... though it doesn't blast out that it's family safe for some reason.
@HootyTheNightOwl I think you are talking about a completely different thing. When you create a post you can choose to indicate the maturity level of the post. If you choose 'mildly adult', then the post will be flagged as 'mildly adult'. If you choose 'adult', then the post will be flagged as 'adult'. However if I choose to indicate that the post is 'family safe', it does not get flagged as 'family safe'.
For example this post of yours is flagged as 'mildy adult' (even though you may not have chosen that, but SW can decide to apply it automatically when it sees certain words in the post)