My Intake is the 'dirty metadata' library.
You know, those books with 40 bazillion tags:
with every possible variant of Science Fiction or Magic.
Tags Loaded with (fans of ) Author names (will like). Anything these folk think will cause THEIR book to come up in a search.
Or the Publisher cant even use a consistent name: We are talking about you Baen Publishing Enterprises (I think my older dead tree books were more consistent)
When you delete a Tag, the DB entry remains, it is just flagged as dead until you run the maintenance (which disturbs the Last_modified and all the OPF backup dates
So I like these to never migrate to the Main Libraries until that cruft has been purged.