This is "working by design" but poorly documented. If you uncheck the boxes "Enable audio alternative path" or "Enable video alternative path" under Network Configuration | Regions you essentially make your edge servers unable to pass media through
them.
What this box is saying is, if you had multiple edge servers in Site A and Site B and CAC stopped a audio/video call from going over the WAN, we are going to allow the call to setup over the internet by going out Site A internet to Site B.
Again, by design, but should be documented.
Thanks,
Richard
Richard Brynteson, Lync MVP | http://masteringlync.com | http://lyncvalidator.com