I believe the most beneficial use of tags is to let the askers categorize their questions, so the answerers can navigate the site easier to find questions that interest them.
Purging all small tags will most probably result in having god-tags. They will become bloated and broad. This will eventually make people hold back from subscribing to them.
If scenemanager is removed, then probably scene tag will host these questions, but the tag scene also hosts the questions that are about, for example, scene design. But if a person wants to answer questions about scene management and not scene design, they will have to dig through a list of questions.
This is no good for answer writers. If the concept of tags loses its use for navigating the site, then I believe it is of no use besides moderation.
Also, considering the latest trend in the community, I say someone can be an expert in scene managers; but this one is just my opinion, not an industry observation.