From an admin perspective, there's not really any additional overhead. From a moderator's perspective, they might have to go look at another forum, but I suspect most of the mods use the New Posts link to see what has been recently posted. So not much overhead on their part either, except for if things need to be moderated, which isn't often (knock on wood).
From an archival standpoint, I could see the benefit of having like posts gathered together, which is why we created the cooking, music, and cnc forums. This was so that content wouldn't get lost in a bunch of off topic posts. We can do what ever the members would like, so discuss away and tell us how you would use such a forum.
To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault