i use tags for annotations and actions: this email i need to reply to. that one links to a story i want to read later. etc. it's not possible to search for that without tags, because those states change and don't depend on the actual emails

AFAIK, you need tags at least for read/unread.

I don't really use tags, but have a few searches to archive email from mailing lists without seeing it in my inbox.

For other usecases, I do as you suggested.