The advantage of the watts in a bagged vehicle is also similar and an advantage for handling. A watts link does a great job, especially over a small displacement, in keeping the axle centered. With the leaf spring suspension in the S10s and Blazers the leaves locate the axle side to side, but they're springs, so there is some slop which translates to a loose feel and poor handling - less accurate relation between the driver and the road. There's likely more theory than I could go into to describe it, but the more predictable the suspension responds to the road the more predictably you can drive.