Some of the info was contradictory. In one section the doctors said the insurance companies weren't paying enough for the procedures and then in another they said by taking cash they were charging less for the procedures than what the insurance company pays. It's a screwed up system for sure.
A Doctor can control his discounts when he negotiates with the patient directly in a cash deal. The Doctor can decide which care costs he can cut and what he can't. The insurance company forces that decision on the Doctor. This may cause the Doctor to lose money on some low margin procedures.