Or if a rider comes off and gets hurt and you have to bring the horse home with out a rider. That happened a couple times when I used to do a lot of CTR. We had riders come off and break arms, collar bones, and one fellow had an appendicitis attack and he left in one of the P&R vehicles, but somebody had to pony his horse back for him.
But more often than not, I'm just packing in camp, a chain saw to clean a trail or just exercising an extra horse.
My daughters like to ride my hot blooded arab gelding, He gets excited and will kick other horses that get close to him at a trot, They are the ones that started watching his ears and if they saw him lay them back, they would reach up slap his ears and tell him to pay attention. Seeing them do that just reminded me of the threats from my mother.
If you put horses on trails like I ride, They learn to watch where they put their feet. I have a friend who trains horses full time for a living. A fellow brought him a TWH and said the horse tripped all the time. Alma took the horse for a month and said he would work on getting the horse to pay attention. He was riding him an hour a day thru rough country. A week or two in the process, the horse tripped and went down and broke alma's leg and his was out of business for several months while his leg was in a cast. So some horses are just a little more prone to it.
One of the selling points for the Fort Ranch's horses is that they babies start life in the rough western Utah desert. From birth until weaning, they run beside their mothers across rough ground. I've never bought one of their horses, But folks swear they are some of most foot sure horses you can own. http://www.fortranch.com/about.html