We have never used moderation in our 4 year-old internal community and we never will. Moderating posts sends the message that you don't trust people to post responsibly, IMO.
Adding a moderator in any space turns on moderation there, meaning all posts will be queued waiting for the moderator to approve them. I can't think of any reason I'd want to introduce that bottleneck and thankless role into our community.
If your documents are open for editing by all, then anyone can add tags. If you want to designate people to add tags to other content, then make them space admins and train them so they know what to do and don't misuse the powers they get along with it -- then you won't have to enable moderation.
Thanks, our challange is that we rarely use spaces. We don't have a problem managing tags for documents - just discussions and the fact that we like some of the discussion features, particularly questions, means that we're reluctant to push all content that needs tag management towards documents.