This info is from the Xray t2 setup book which can be downloaded from their site.
Effects of Rear Ball Diff Adjust ment
· Car understeers slightly at corner entry, but makes the car more difficult to control at corner exit (powerslides).
· Increased on-throttle steering.
· Usually better on high-traction surfaces, but may decrease rear end stability at mid corner.
· More stability mid corner and corner exit.
· Understeer on-throttle.
· Better on low-traction surfaces or in conjunction with a front one-way.