It means that you can choose to buy a plan that meets what you're looking for. Such as, Massachusetts has a shit ton of things that have to be included in a policy: pediatric dentistry, fertility treatments, etc. I think Mass has like 50 mandates of things that an insurance company must cover. Fuck that. I want to shop for a plan that only covers what I feel like having covered and am willing to pay for. But, the dear lknow-it-alls who run this state want to force everyone to have the same coverage.

If you could buy a plan from say Ohio that was just basic and covered what you wanted covered, it'd cost a lost less. Clearly someone isn't going to select a plan that restricts them to providers in another state. You'd probably see an out-of-state company work with an in-state company to access its network for a fee, at least until they could establish their own provider network. But it'd still be a lot cheaper than having everyone pay for a gold-plated policy that they don't necessarily want but have to buy if they want insurance. And in Mass, you have to buy or you get penalized.