Why do some horses only have shoes on their front feet?

If you look around at horses, you might notice that some horses only have shoes on their front hooves. There are two reasons for this:

1. The front feet take more of the horse's and rider's weight, so some horses may have strong enough hooves to not need shoes on the hind end, but still need them on the front.

2. Not putting shoes on the rear hooves reduces the risk of injury if horses get into a fight out in pasture.