After installing the body lift. There is now a gap between the body and the frame. It will be noticeable above every wheel. This gap will also allow unwanted mud and debris to enter the engine compartment. The guard will fix this and make make the truck look cleaner, espically in the rear when you can see straight through to the other side.
From any 4x4 store, you can order gap guards. They will run around $35. They will come in thick rubber and buttons to snap onto the body.
Installation requires a drill. You line up the guards starting at the middle, then drill the first hole. Then proceed on until you reach the outer edges.
There are already some rubber guards in the front fender well. I left them there and installed mine right up next to them.