Usually, riders use spurs to get a better and quicker reaction from the horse. Spurs are used to encourage your horse to react faster to your leg, as by nature, horses can get dull to your leg. Spurs can be a great tool to help the horse to react with more precision, without more pressure from the leg. A highly advanced dressage rider, for instance, may want a more precise reaction from their horse when riding tempi changes or pirouettes. In addition, some horses that are very sensitive can benefit from the use of spurs. When you use your spur gently on a sensitive horse, it's a clear and light aid for them, and thus works as a great reward.