Other than make the posts unavailable to normal users (or guests?) what does putting a post to private do?

(i.e. what I'm really asking is, is the post just as visible to mods as it was when it was set to public? or does it mean only users in the "Users In This Discussion" can still view the post?)

The reason I'm asking, is because I recently put a post on private, and was wondering how that affects how mods see the post, and actually, there were no "users in this discussion" other than myself, so if putting the post on private means only those users can still view the post, that means no one can currently see the post...