It's always a good idea to get approval from the moderators of the forum you want to post a thread in, particularly if it's a community project like the CCAT. For example in the RU forum, if you were going to make a thread that gave points to people, you'd most definitely need the approval of the moderators before doing so. However, most small discussion threads, such as the Garchomp thread, do not need approval. If you have an idea for discussion that is not explicitly covered by another thread, it's usually safe to assume that you can create a thread for it.
If you're OP is well written, and the content unique for discussion (without breaking any rules) it's safe to assume you're free to post it.
Just know that your threads will always be 10x better if you discuss with a moderator beforehand on what you want to talk about and how to structure the OP.