I asked a question about the use of 以外 recently and tried to create a new tag "particle-igai". It was rightly removed because 以外 is not a particle, but it got me thinking about how we use tags.
Many of my questions just end up with the generic "grammar" tag, because there isn't a tag relevant to what I'm asking about. How useful is the grammar tag? If I have a question, I'd never think "I know, I'll search all the question that are tagged as grammar and see if any of them answer my question". But if there was a tag named "igai", I might do just that.
Even simple things like だけ have no tag, and nor does the ever popular という to name but two. Just doing a search for だけ is useful but not ideal since loads of search results will have incidental uses of the particle and won't actually focus on its usage. Would it be useful if we started creating tags for things like this when users post questions? Or is it too late to worry about it? I shouldn't think anyone has the energy to go retro-tagging all the old questions.