This is useful to aid navigation for users that follow a particular navigation path, but there is another forum more approrate to their needs. (I only have it when there is a top level category that could fit in another forum, to redirect the users who have gone into that forum to the top level cat) 

At a finer level, it would be good if Administrators had the ablity to point a post at another url. This would mean if a user clicked the link post to open it, it would take you to the post in a different forum. This way you could have the main post in the most appropriate forum, with similar posts, but if it would also sit well in another forum you could have a redirect post in there as well. (Arrowed icon like the forum redirect)

This again would ease navigation for the users and help clean up any ambiguity as to where a post should be.

For a contrived example for this forum: You may want to put a post both in "Company News" about a new release which improves the ease of migration, but also in the  "Forum Migration" Forum for that version...

Cheers
Jeremy