There are cases where the hooves might get too short, which will cause the horse to lame - you couldn't miss that sign, I suppose. If your horse trips a lot during rides on hard roads, that might be another sign.
Nowadays there are so many good alternatives, that shoeing should be avoided whenever possible, since horse shoes do great damage to the inside of the hooves and can cause injuries. Most horses can do well all their life without shoes, there are simply to many owners that don't have any clue and shoe their horses because the other riders say so, and the farrier says so, so it must be true... You get the idea.
Especially if your horse is in the paddock most of the time, you should prefer horse boots over horse shoes, as you can remove them after the ride. Nowadays horse boots are so well designed that there are great designs that can even be used in competitions - no shoeing needed anymore. They aren't yet as popular as they should be since many owners simply don't know enough about the topic, but I hope to live until the time where metal shoes become history.