Use case #1: we would like to have a “Jobs - Resume” category and would allow only ONE topic to be created in that category by any user.
Use case #2: we would like to have an “Official company pages” category and would allow only ONE topic to be created by SOME users (btw, is there any way to allow only users with a particular badge to post to a particular category? - if yes then we would grant a Company Representative badge and make a category where only holders of that badge can create topics, and preferrably would limit them to only one topic per user). This can also be one of ways to monetize with time.