Do you mean attach as a tag?
The only reason that I don’t think tags are a good solution is that I’ve never seen any evidence that anybody pays attention to tags. They never seem to get referenced inside a thread. Last October What Exit? asked if anyone was using them and got no answers until one question four months later about their not working.
I usually forget they even exist.
I’m on team Leave a Relevant Thread Open, even for dopey bumps. Unless it becomes problematic in a way that it can’t be corrected by moderating individuals (rare) or is an expired topic (Hillary!), threads should be left open. For newbs, bumps, spammers bringing to light previously unseen discussion: Leave open: potential more content. Close: no more content forthcoming.
I do. For instance, if I’m looking for a thread about books, the tag means I don’t have to wade through all the threads about movies and food.
I’ve found the ability to automatically watch or mute all threads with a given tag rather helpful.