In-network arrangements is as if the doctors were accepting Groupon (a group coupon) — will the lower reimbursement they receive be offset by more patients and when is the point of diminishing returns (when too many patients makes it not worth it as well).
The difference between health care plans, and this impacts the earnings for doctors as well, is the breadth and depth of the network. Consumers might pay less for a network that might not have as much choice with, say cancer care, and a doctor who belongs to a network with a breadth of services might not burn out having passed that point of diminishing returns.
Basic fact sheet from Healthcare.gov here. It can be confusing to choose ahead the type of medical professional you will need. For example, here she discusses using a pediatrician or using a general practitioner for you baby that depends on your network.
Lets be realistic, that health insurance isn’t an upgrade to 1st class if you can only afford coach. The network will lose and collapse leaving you will no care, ala the “Groupon” scenario or deep discount scenario.