They offer a check on healthcare providers that want to over -treat and -prescribe to charge more money, or doctors that go rogue with whacky ideas. Since the general population doesn’t know much about medicine, doctors would be able to prescribe all sorts of illegitimate treatments if we didn’t have a body making sure that their recommendations were legit.

My dad can't get a medication that actually resolves one of his health problems because it's not on whatever list of medications his insurance company has for that issue. Even though his doctor prescribed it and it worked up until he got a new insurance. Now he has to use some other medication that barely helps. Insurance companies are bullshit. Doctors should be reviewing what other doctors are doing. Not some office peon who probably gets a bonus for rejecting claims.