Not sure if what I'm saying has been said...I apologize if it has I didn't read through all of them.
I really don't get it while a rider is in a course, I feel like it is a distraction and the rider should not be focusing on what they are doing with there butt but instead the course, the strides, ect.
I understand why riders do this in on the flat in hunter classes. Going in a half seat during a hunter class allows the horse to move more freely and open up there stride. Thus they look better, so they can place. It actually does work because less weight is on their back.