Giving preference to the spinning wheel is a by-product of the slipping differential. At highway speeds if you have a locked differential, it puts a lot of twist on the axles when you make a turn, because the inner wheels travel a shorter distance than the outer wheels. The slipping differential lets the outer wheels “free spin” at a faster rate than the inner wheels so that the axle doesn’t have to twist.
As I understand it, with Subarus, they work like a normal AWD under high traction conditions, but when the drive train senses much faster free spinning than expected under high traction conditions it locks the differential.
