The documents versus forums thing makes sense. I do have one question about it though which is that, if I am in a Forum, and I select a category, I can't then choose to see only the archived threads from within just that category it seems. I have to see all the archived threads from that whole forum.

For example, we have a forum for a team we made up called The Deadly Droppings. Within that we have categories for "Coaching & Strategy," and well as "Participation." There is a topic/thread I made archived in "Coaching & Strategy" called "Jose Mourinho." When I select the category "Participation" I see the normal posts in that category. But then when I hit Archived to see all the archived topics/threads, it shows me "Jose Mourinho." 

So, it seems like the categories don't carry over as an organizing tool to the archive. If we had a bunch of archived topics, I could see this being way more of a pain to navigate than if you could at least narrow it down by category.

I tried making a new archived thread that was in "Participation" and then looking at the archived threads and trying to select a category, but that just took me back to the non-archived forum category, a.k.a. the regular one.