That final payment combined with the trade-in value is structure such that the dealer is the only party that will give you a good price on the vehicle and you'll get a new car instead of buying out the old one.
I'd noticed that everyone seemed to be spending more on cars than I felt was wise. After discussing it with a friend with one of these deals he said he basically felt trapped into buying a new car after 3 years.
Yes. The deal is dandy if you plan to buy every 3 anyway. If you don't, that is the big downside. (Or if you want to drive a lot of miles, etc). Buying a car every 10 years is a lot more fun than every 3..