I believe its because many RV's have too small of jack pads in the first place. I see some 6-8" round pads that are bent up on the edges from gravel then only a small surface is touching the ground. Our HWH jacks have square pads that are 10" on each side that provide an area equal to or greater than the front tire contact patch. Have never used an additional pad. What really gets me is the RV manufacturers that skimp on jacks in the first place by installing only 3.