Question: Where - except for a SIP REFER - is this application of use, why not simply use Dial(), maybe together with a Local channel?

Answer: For example, a SIP provider offering DIDs, you want calls to go to a colo box and then be transfered to other locations rather then waiting for the DID provider to update routes, by using this you save headaches with 1 way audio due to tracking firewalls not being able to track asyncronious SIP and RTP paths, and call delay if you and the colo are in different countries. Downside to doing something like this is you incur a slightly increase call setup delay while the call is bounced between servers, but no one will ever notice since most people take a few rings to actually answer.
C'est ton cas ?