Prob puts him on the court a bit more. But they play different positions. Both are primarily defenders, but Pons on backcourt and Walker in the post. Directly, this affects the rotations and PT of Turner, Bowden, Johnson, and even Bone.
I may be in the minority here but I absolutely cringe when the ball gets passed to FULK in the post. It is essentially a wasted possession; however, FULK does a nice job of being that high energy guy and never giving up on a play. It is hard for me to really gauge how much Walker has improved due to limited minutes this year. I do like Walker better as a low post defender.