Breakover is how quickly the horse is able to pick the foot up after putting it down (that's not exactly right, but I can't think of the proper way to describe it...someone else will do a better job). A horse with long toes is about like a human trying to walk in clown shoes or swimming flippers, it's impossible to get proper leg movement and it puts a lot of wear and tear on the tendons if the horse is having to work to get his foot picked up.
The horse with had with Navicular (was diagnosed at 5 by 3 different vets due to really crappy shoeing...super long toes, no heel, etc) did really good with those Natural Balance shoes. They had the toes sort of squared off so that he would have a really easy and quick breakover. With that, and meticulous hoof care (never let him go even a week too long), he was sound for work until he was 25. Granted, the last few years didn't involve hard work, but he was still being ridden frequently and worked lightly on cattle.