The word "clutter" appears to be distracting people. The core principle is that a forum needs to pull its own weight by adding enough value to FT to justify its inclusion in what is already a pretty large Forums menu.
It's no more complicated than that.
Value can be demonstrated by post count, provided that those posts don't have somewhere else that would be a better home for them. Value can also be demonstrated by posts with focused content that has no good home anywhere else on FT. In this latter category are the more obscure programs and destinations. However even obscure focused content must meet some threshold of utilization to warrant inclusion in the Forums menu. The less focused the content, the higher that threshold should be, IMHO.