in discourse, a category is completely separate from its subcategories. while one can imagine something more related or interconnected.
two of the most annoying cases:
if you suppress a category from homepage, none of the subcategories are suppressed from the homepage! and you should do this for all subcategories one by one.
in the admin analysis panel, if you want to check for the number of posts in a category with its subcategories, you can’t! because number of posts or topics in a subcategory is not summed of in its corresponding category.