For example, when #off-topic was created, it was made to include games, memes and other stuff not related to byte, but it just sits in one topic.
We could add subcategories to #off-topic such as #off-topic:memes, #off-topic:games and #off-topic:jokes which would let users find exactly what they’re looking for.
There could also be subcategories for #idea such as #idea:graphics or #idea:teams.
Subcategories could also be added to #promote-yourself for say #promote-yourself:youtube or #promote-yourself:instagram.
Basically to sum up, subcategories can just allow people to find what they’re looking for much easier, and could also allow users to completely ignore specific subcategories if it isn’t something they’re interested in!