I would say it is illegal to report that services were performed in a location other than where they were performed. It really doesn't "streamline" anything, that is just a way to say "I don't feel like doing the necessary paperwork to make sure the claims are being billed properly".
Sorry, that's probably a little harsh, but it's true. I've seen many providers like this. But you can also say, if he/she gets audited, the insurance carriers could determine that they broke their contract with them by not reporting the satellite office and billing as if services were done in the main office and terminate them.
Just to have some backup you could call a local provider rep for any insurance carrier and ask them if it is ok to bill satellite office as main office.
Good luck,
Michele