It depends on your risk tolerance too. And everyone is different. I only got two interviews after applying to 32 programs. One interview was match and the other wasn't. I received an acceptance from a non-match program which has $80K/year tuition and required me to drop out of the match upon acceptance of their offer, which I did. Due to the Post 9/11 GI Bill, the match program would have had no tuition and a $12K/year stipend but the non-match program tuition would just drop to about $60K tuition a year with no stipend. I even got a letter from the program director of the match school stating "I really liked your interview." But even with that there was no guarantee and the program director could change his mind if he liked someone else more at the second round of interviews as I attended the 1st round. Or where was I on the list he "really liked"? 1st, 2nd,3rd, 6th? Who knows. There were only 5 positions available there. Imagine how dumb I would have felt if I turned down my acceptance and then didn't match because I was 6th. When I dropped out of the match, the match even called me to verify. I imagine I was probably ranked well at the match program, but I had no guarantee and the program is not allowed to tell you where they ranked you in the match. A letter such as the one received by them is the best they can do if they're following the rules. I will forever wonder what might have been and quite likely lost a $140K+, plus interest, by accepting the non-match position. I will forever have a somewhat bitter taste in my mouth by being "forced" to make this decision. But I am going to be an orthodontist, so how bitter can I really be? I need to be clear. Non-match acceptances are NOT easy to get. They are NOT handed out like candy. If you get one, you still won the lottery.
Playing devil's advocate, I'd be a liar if I said I never thought about the following. I am positive that many accept these positions at non-match schools and then do not drop out of the match like they're supposed to. When they match, they notify the non-match program that they now decline the position and simply lose their deposit. My school's deposit was $5k, so by all means, not a small chunk of change. But this maneuver could backfire on you far worse than just loosing the deposit. Still I imagine that, most of the time, it probably doesn't. Program directors do talk, but it would probably be very difficult for the program director at a non-match school to know where you matched, especially since they don't participate in the match. But if they were able to do so, and divulged what you did to the program director of the school where you matched, you might find yourself out of a position and on a black list. A maneuver like that may prevent you from getting in anywhere even in future cycles. For the record, I doubt a black list really exists though. Also, if the program director of the match school ranked you high enough to get matched, they probably did like you and want you. Given that the match would be over for that cycle, if the match school reneged on their acceptance of you due to your poor ethics, imagine how low they would then have to go on their acceptance list post match in order to fill your slot. In all likelihood, you will still probably keep your position but your program director and the other faculty would probably always view you as the unethical kid who needs to be watched more closely. Not a good place to be, and may indicate that your career will consist of more unethical decisions in the future. That being said, if you were able to keep your spot, despite your tarnished image, I imagine you would frequently think to yourself how dumb you would have been had you accepted the non-match position and how much you saved by rejecting the offer that non-match program tried to "force" you to make. Additionally, should you not match, then you didn't loose anything. Not only will you not feel any resentment against the non-match position which you accepted, but it will make you even more grateful for that program's acceptance.
So there's a risk tolerance part of the equation and also an ethics part. How will it make you feel about yourself to do this? For some, it's an easy answer based on ethics alone. For others, they will justify it as the "cost of doing business" and claim that it is the non-match programs that are being unethical. After all, is it ethical to force a student to lose a shot at saving $140K+, plus interest, to justify getting the best students they can? I believe it is unethical. I say this because I doubt, if it were them, they would want to be put in this same position. That being said, no one put a gun to my head and forced me to apply to this school.
It appears that the legal repercussions are minimally a loss of the deposit. But is it actually a legal document? We make our patient's sign all kinds of documents that would not hold up in court. Would it be ethical/legal for these schools to keep the deposit and then additionally defame you by contacting the program director of the school where you matched? Could you sue the school for defamation and additionally get your deposit back? Do you even want to put yourself in this stressful scenario? These ethical/legal scenarios are debatable and we will all need to answer them for ourselves.