I'm an admin in our own instance (mujico.org), I have seen some posts that need the NSFW tag but I can't find a way to put that tag, There are some posts that are not NSFW and I would like to remove that, that's it.
I remember looking into it back when lemmynsfw was brand new and flooding all with un-nsfw'd porn and the devs seemed to be explicitly against giving mods the ability to edit posts, which NSFW tagging kinda falls under.