Leveling

What he said^^^^^^^

Plus....jack pads help keep jacks from punching holes in asphalt/dirt/mud/grass
whatever the cg site might be

Some use pads to increase the footprint on the ground, to help level the MH, especially if the ground is soft. Some use pads to get increased lift, when needed. The less you extend the leveling jacks, the more stable the MH will be, as there will be less flex in the jacks themselves.