The urge to introduce a 'missing' category is often strong. But a new category that references just one or only a few pages is not worth much. In these cases a common Topic Page should be enough, and given a more general category (if at all, see Please Please Dont Categorize Every Page On Wiki).
There should be a guideline for introducing categories.
I propose that if you want to introduce a category, then you should first pull together some (say 10) pages that already fall into it. And then you can add the category. This was the advice I was given when creating Category Wiki Progress.
See original on c2.com 