A horse is a brain on four legs. A horse is not a body with four legs. If you want a horse to do anything you should have a conversation with the brain.
My take on this concept is that when a horse is first started, having a job to do can assist a horse to get comfortable with just carrying a rider and following some direction.
I believe that training should involve working through as many challenges as practical to help a horse cope with life as a horse. For this reason, I will even invent challenges that have no practical purpose just as an excuse to grow my friendship with a horse.