I've noticed that often I have forums where it would be useful to make them read-only—however, occasionally, there might be a good post for that forum instead of its child forums.
For instance, the Dream Forum I have isn't supposed to receive posts of dreams to be analyzed, but its child forum, Dream Analysis, is. The Dream Forum should, however, be used for posting conversation about dreams (not relating to specific dreams). It would be nice if people who tried to post there at least got warned before that dreams for interpretation should be posted in Dream Analysis instead (and give them the option to switch while viewing the warning screen). I'd rather keep this forum as a parent if I could.
I do not, however, want this functionality for every parent forum, I have, but just one to five of them or so. I know back in the day it was sort of like this for all parent forums.
Another way to solve this would be to add the ability for forum owners to moderate posts in a different sort of manner. Rather than simply approving or disapproving, they would be asked whether to let it go there or in a child forum instead (maybe have a new link in the email for each child existing forum).