During riding you can communicate with your horse most effectively if you have the proper interface. The rider being astride the horse's back with no saddle or pad between is probably the best way to communicate and hear from your horse - but not the most practical.
The bareback method offers a superior communication path by way of muscle movement and leg pressure, but the rider can slip off easily, it's kind of hot and sweaty, and there's no good way to carry items. In addition to that riding takes extra effort to ride bareback for a long time, which wears on the rider.
The bareback pad method features a better seat and allows the rider to communicate with their horse effectively, but again, there are some drawbacks. Bareback pads can be hot and sweaty and there are few, if any good places to tie off bundles such as camp gear and the like. Also, the bareback pad is not meant for extended riding. Having a nice flexible treeless leather saddle with a secure seat is probably the best way to ride. because for both your horse and you, both the performance and functional factors are significantly enhanced.
Treeless saddles are very flexible. There is less material between the rider and horse then a treed saddle, much like the barefack pad. This arrangement improves the communication from leg pressure and muscle movement. The flexibility of the saddle allows your horse to move side to side freely. And your horse doesn't feel pressure from any of the saddle parts poking into it's back causing pain and discomfort. The pain and discomfort from saddles is responsible for more performance problems then from any other source, other than lack of training.
Without a rigid tree in the saddle, riders can feel the horse's back and leg muscles flex and relax, even their horse's breathing. You will feel the increased comfort, fit, contact and communication between horse and rider. If you grasp and wiggle the SS on both sides of the saddle skirt from behind, it will twist easily from side-to-side showing that the skirt is flexible. Gripping the back end of the saddle skirt, it can be folded double-back onto itself, but don't do that because it could put a permanent crease ing the leather.
Sport Saddle riders are enjoying success in all areas of riding - schooling & training, endurance and competitive riding, barrel racing, trail riding, show and just plain fun riding. Your horse's performance improves and the satisfaction you derive from your sport goes way up.