A horse shoe can serve many purposes. It can bring luck to the household over whose door it is nailed. It can be used as decoration or as a wall hook. It can be nailed to the bottom of a horse’s foot to protect the hoof or add traction to the movement.
(It can be very controversial. See The Barefoot Horse)
“In earlier centuries, Cobblestones were a uniform width to fit a prescribed distance between the toe calk and inside heel calk of a commercial horse’s shoe. Today, paving stones are set close together and mortared in place. In the horse’s day, the stones were set in place with a few inches of space all around each paver. This was especially important for a street with any sort of slope.
The horseman who did not have his horse regularly shod would find the horse struggling to pull a load up a hill, since if a calk was worn, or a removable calk was missing, the horse couldn’t grab onto anything.”
The horses of Prague and Budapest were shod with a heavy shoe and then outfitted with a rubber heel calk to help them keep traction on the cobblestone streets. It remains to be seen how raising the heel of the foot that high affects their navicular alignment.
The heel is not so high when the hoof falls over the cobblestone in such a way that the heel calk falls in a crack between the stones, but it can be very high if it falls on the top of the curved dome of the stone.