One of the biggest complaints many had about the Jim Leonhard/Eric Smith starting safety combo is how little they complimented each other. They essentially did the same things.
They were reportedly responsible for the team lining up in the right spots and making sure everybody knew what they were supposed to do. They had the option of changing things they did not like. They could both hit hard and were best against the run. Neither was very good in coverage. Smith's lack of athletic ability relative to top tight ends is well documented and has been exposed frequently this year. Leonhard's size and lack of speed made him a human mismatch in coverage against big, fast tight ends despite all of the other things he did well to compensate.
Brodney Pool has once again become a starter. He might make the safety mix more diversified. Many voiced a belief that Pool should have started over Eric Smith.
Pool is probably the best cover safety the Jets have. Leonhard could still play the run, while Pool could carry more of the load in coverage. People wanted Smith to sit because Leonhard is a better player and a bigger playmaker.
Last year it felt like the Jets played their best pass defense after Leonhard left the lineup. They missed Jim in other ways, but they shut down Peyton Manning and Tom Brady in the postseason.
The new safety duo might actually compliment each other more than the former one. Pool can take more coverage responsibilitis, while Smith can play the run instead of having two guys who do the same thing well.