While that might work for some, if there is a subforum they can browse by topic they may run across things they are interested in. Either with helping or something that has info in it they did not know they needed.
That is the beauty of a forum. Its hardly complex, in fact its the opposite. Just like you have separations for everything else in life, you separate by topicality here. In your dresser at home you have multiple drawers. Socks, shirts, etc. So its easier to find stuff. Same concept.
If someone is looking for help with a particular printer and they are reading headers, they might run across something else that applies to their printer that they are interested in. If things are all jumbled together in a single forum that is less likely to happen.
Thanks! I was looking for a top level item so I did not notice it there.