It stops the truck from cutting out four cylinders, leaving it constantly in eight cylinder mode.
Just a personal preference of mine. It does seem to help significantly (at least to my mind) with acceleration and torque. I never liked driving around a half ton pickup with four cylinders. Another thing it supposedly does is stop 5.3 engines from developing oil burning issues over time, but my truck is so new that has not been an issue.
Just my little personal rebellion against these crazy CAFE standards.
