It's only valuable in so far as people think carefully about where they post, and post only under the appropriate topic.
This is fine in theory but, in practice, fails on two points:

Lots of real-life problems don't fall nicely into exactly one topic;

It is only too obvious that there are far too many users who are incapable of choosing an appropriate topic :-(

So, while it's a great idea in principle, I'm afraid it won't work out in practice - unless the forums are extremely heavily moderated...!

:-(