I want to reorganise my categories and tags. If I delete a subcategory, the posts in that subcategory will go to the default category. Wouldn't it make more sense for them to at least go into the parent category instead? Top-level categories would still go into the default category, however. Likewise with tag-to-category conversion.
Ideally, I'd like to be able to specify which category the posts should go into no matter what level they're at and no matter how they're removed. Otherwise, I have to plough through each and every post in a given category and recategorise it manually. Such a chore!