Merge some forums?

I guess I am in this rather late, but before I would have merged forums, I would have checked the SEO value of various forums. Where they rank? What keywords? Traffic wise? And so on and so forth. I am all for merging forums, but sometimes once they are established and indexed, you can kill off a good bit of traffic by dissolving them into another. This is just something I dont see mentioned in the ongoing conversation. And something people tend to forget about. I have learned the hard way before by killing off one of my best keywords when merging forums together