Oh, hello Kanata!
What's your reasoning?
Roleplaying and Quests attract a different kind of people as it requires a different amount of effort in order to participate, and splitting those up into a separate thread my allow people to easily find the content they are looking for.
Also, it is still relatively easy to do so as the forum is still relatively young, and there aren't that many threads to actually move, so it isn't a logistical nightmare.
I assume you want to attract more people to this forum, and this quality of life changes are easier to be done early on, later on it wouldn't be worth the trouble with potentially hundreds of threads SB have for example.
You may also want to split artwork and music as those are separate things.
It is not necessary per se, but if you want to divide everything neatly into strict subcategories at all, it is better to start early on.
Also, may want to split between fanfiction and original fiction. It is not strictly necessary, but as I said, moving threads is easier early on, it will not be trouble either.
I think those 6 categories pretty much cover all the content you probably want to have on this forum.