With Fess helping out with defense in the paint, it makes slashers like Lebron and Wade hesitate, and it means that the defender can guard the shot rather than the drive. It makes a difference. Fess either makes the slasher finish a tougher shot or make a tough pass in traffic. Plus he can actually box someone out on the rebound.
I am sure somebody mentioned it but not only was Jefferson unable to hit the broad side of a barn he did not bother to contest hardly any shots by driving Heat players. If he does not want to play defense he may see his minutes reduced a lot once Memo comes. back. Hopefully his benching will cause him to pick up his intensity of defense. Also hopefully this game will put Fes back ahead of Elson on the depth chart.