Only people that are bad at math.

Whether or not this is a good deal depends on a ton of different variables and everyone's case will be slightly different. How far are you from the end of the contract? Do you have an old grandfathered plan? How much is your current phone worth on trade-in? What will your new bill be compared to the old once you factor in buying a new handset? That's just a start
Some people will save a ton, others not so much, and some still might pay more. The ones who will save in the long run far outweigh the other groups though.