I have done some research and I found that if you ride your horse bareback to much, or for a long period of time, your horse can get sores on it's back for the weight not being distributed the right way. When I fully train my horse bareback riding, I will not ride him bareback all the time since it can be bad or painful for the horse. Some things you can do while riding bareback to help spread out your weight is to use a bareback pad, they are softer on the horses back and more comfortable for the rider.