By curiosity, which of these tables (having 0 rows/entries) can be considered unnecessary?
I know that some were created by plugins, some are there be default:
qa_categories ← I am not using categories, that's why this is empty.
qa_categorymetas ← same
qa_messages ← I am not using PN that's why this is empty.
qa_postmetas ← what for?
qa_tagmetas ← what for?
qa_usermetas ← "Plugins etc... can use qa_usermetas for any meta information relating to users - see qa-db-metas.php." Clarified.
qa_usernotices ← what for?