The only con I can think of: it's yet another forum to think about.
Lots of pros, though. Personally, I like having more granularity in the forums so I don't have to wade through 997 meaningless posts to find the 3 on the topic that I really care about (or trying to find something in a completely illogical location, like when the British railways were under the BMI forum). I used to have a list of airlines that I followed every day, but found it was taking 3 hours just to get through the new posts and comments, even skipping most of them!