Dealers are subject to an annual inspection of their books. As a C&R holder I'm not sure if you will get any inspections at all, unless BATF feels you may be violating some provision of the law. As an owner of a machine gun, you'll probably never see BATF. I've owned machine guns since 1966 and never had an agent visit me. They aren't really interested in legal owners of machine guns, but those who try to circumvent the laws.
Remember a C&R does nothing at all towards helping you acquire Title II weapons. The ONLY advantage, as mboylan stated, is that if you purchase a C&R eligible firearm from a dealer in another state, it can be shipped directly to you instead of going to a FFL in your state first, and then transferred to you. That will save you the cost of one transfer, about $100 is pretty standard, and several months' time in processing the second transfer. There's nothing special about a C&R helping speed up a transfer, and if you buy anything NOT C&R eligible, it's worthless to you.