A huge amount (the majority, I believe) of health care costs in the U.S. are spent treating chronic illnesses. Chronic illnesses are like hunger--you know you have it, and you know you will need regular treatment for it. Buying medicine in advance is how chronic illnesses are treated.

Medical emergencies are a popular counter-argument to the idea of greater market clarity in health care, but the reality is that most people encounter the medical system in non-emergency situations. They have the opportunity to shop around for these--but often don't, because they don't have the information or incentive to do so.

As for emergencies or unexpected costs--that is what insurance is properly for.