He doesn't have to play any physical defense down low or fight over the tops of screens outside. He's just sagging back and letting Giannis have several feet of space when Giannis is floating around the perimeter or the free throw line.

Add to that that Blake is (and has been) a better passing big man than most of the bigs in the NBA, and he can really supercharge the Nets offense even when he's not doing the scoring just by nature of his really smart ball movement.