It seems to me that the offense runs better when he is on the field, as opposed to Singletary. Or, at least, that's how it appeared to me during the Washington game.
That is obvious, but it more has to do with the play call and execution. It's one thing if you throw the ball beyond the first down marker and Washington defends well and knocks it down. It's another to throw the ball short of the sticks on a play call that really only has one route.