In 2018, Suh's money moves from guaranteed to un-guaranteed. Meaning that the Dolphins will be in position to blow up and rebuild if their superstar acquisition has been less super than planned. The The Dolphins are all in on Suh- for exactly 24 months. If he hasn't helped Miami dominate by then, he and Williams will both be cut loose and the team will go out and find a new approach.
In the end, the Dolphins have effectively traded Lamar Miller and Olivier Vernon for Suh. Letting OV walk may have been wise, given the contract he received in New York, but the Dolphins only had to resort to that option due to the mountain of cash they have committed to Suh.
So the message is clear: Miami wrote you a blank check, Suh. But it comes with an expiration date. Dominate or be cut.