A horse is a rather expensive lawn ornament if it is not used for anything. I believe that humans and animals need a sense of purpose to their lives. Both become bored with inactivity. For most of human history horses were employed in working roles and this was not an issue. However, in modern times horses have been supplanted by mechanization and the question of what you plan to do with a horse is a real one. There are a lot of possibilities and in the end it is what you find enjoyable and the aptitudes of your mount.
The total population of horses is down from its peak in the early 20th Century but in my own state of Maryland the 2010 Maryland Equine Census showed a total of 79,100 equines of various types, including donkeys and mules. For a relatively small state and an animal whose working utility has been mostly been supplanted those are still significant numbers. It is clear that many people still have horses in their lives.
In my series on equestrian sports and activities I will look at the various things riders do with horses. However, I am not covering all of them. The total list is a very long one and includes forms of English riding; such as fox chasing (hunting), dressage, eventing, equitation and other types of showing, show jumping, side saddle showing, steeple chasing, Thoroughbred and Arabian flat racing, polo and polocrosse. There are forms of western riding; such as, various rodeo events, barrel racing, reining, cowboy mounted shooting, cattle cutting, western dressage, western trail riding and western equitation. Other riding that might be in either English or Western, unless otherwise prescribed in event rules, includes competitive trail riding recreational trail riding, therapeutic riding, endurance riding, mounted archery, and obstacle course riding. Let us not forget historical reenacting, various forms of driving, draft horse pulling, mule showing and jumping, harness racing, recreational driving, vaulting or trick riding, mounted police service, mounted search and rescue work. My apologies to you if I omitted something else you love doing with a horse.
I am mostly a trail rider. I find it a relaxing break from and stresses and strains of modern living. However, I have engaged in other equine activities as a participant or spectator and have friends who have done even more.