Well, I can tell you what it is for. Some horses hooves have more of a cup shape to them than others. Some are more "flat-footed". The ones with a shallow hoof are more prone to painful stone bruises because the more sensitive frog of the hoof is closer to the ground. (Yup, you read that right, the wedge-shaped center of a horses hoof is called a frog) Also if a horse has already experienced a stone bruise, a pad like the one on your horseshoe protects the hoof. Farriers (guys/gals who do horseshoeing) can do a lot of corrective shoeing to help make life easier for the horse.