That's the reason it gets so much criticism... there isn't really a point. If you lust for more knowledge of the body, then you may get that, but this might be the only advantage. Like I said, if you want to do oral surgery, it won't save you anytime.
Traditional Oral surgery: 4 years dental school + 6 years residency/MD = 10 years
Case DMD/MD and Oral Surgery: 5 years DMD/MD + 1 year GS internship + 4 years oral surgery certificate program = 10 years
I could only see the program being valuable if you really have NO idea which career path you want to follow. At the end, you can either pursue a residency in a dental specialty or a medical specialty, which is one of the plusses.