As a Journeyman Farrier and having shod horses for 37 years , I have found you shoe horses for 3 reasons. The first being protection or when the wear rate exceeds the growth rate. The second is to enhance what the horse is doing, a reiner wears sliders to help him slide or an english horse wears a weighted shoe to give him more action, etc.The third reason is for theraputic reasons such as conformation faults or injuries. If you have a horse that has none of these requirements you`re lucky and should keep and enjoy your horse!

As with many of the questions posed here, this one has two answers.

Much depends on the terrain, if the horse is being used or not, the strength of the horse's feet, what the horse is used for, etc.

While living in eastern Washington, I had a mostly rock free pasture and rode mostly in the forest, where the paths were padded with pine needles and grass, so I left a couple of my horses unshod. However, if I was going to take them on a long trip, such as the Pacific Crest trail, I would shoe them.

I think this is an age old question with no one simple answer.