My boarding barn has a policy that hind shoes are only on when a horse absolutely needs them. In fact we have lots of horses that get shoes pulled for two reasons: 1. In the field they are unnecessary unless for soundness issues and can be dangerous to other horses (and expensive to keep putting back on!)
2. When we're training a horse we don't want to worry about having the extra danger to us and equipment of metal shoes on a 1000+lb animal.