The low position will allow the car to roll more and keep the car in a turn longer, increasing on-power steering. The high diff position will give the car a flatter and more responsive feel. It is also possible to change the balance of the car quite drastically by offsetting the height of the diffs from front to rear. Testing has shown that maximum total steering can be obtained by running the front diff low and the rear diff high. For less total steering do the opposite. For less overall traction run the front and rear diffs in the low position. For more overall traction, do the opposite.
I got this from a Facebook post in the B74 Nation Group.