Martial Arts by definition are the "war" arts. Even though a "good" Martial Artist "hopes" to avoid war and/or a lethal self-defense situation, it is the #1 situation that a Martial Artist should be prepared for.
Sparring builds muscle memory, coordination, endurance, courage, humility, reflexes, pain tolerance, validated confidence, and more of the things that we would need if we ever have to physically defend ourselves.
When we spar we learn that talk is cheap. We learn to attack. We learn how much strength, pressure and speed is required to truly stop a strike, grab or takedown. And most importantly, we learn how good and bad we truly are.
Contrary to the efforts of many, we SHOULD NOT get injured or INJURE others when sparring. The pace between two sparring partners should be kept at a pace that both can handle and never over whelming for one. When both sparrers are swinging wild and afraid, nothing is learned and only luck will determine the outcome.
Hard contact sparing should be done in safety equipment and by experienced, disciplined, controlled partners only while under the supervision of an authority that they both respect above their own egos. Hurting someone or getting hurt in sparring does not make us a bad @$$. It makes us the uncontrolled jerk who no one will want to train with eventually.
A sparring match between Martial Artists can not be sloppy and desperate. It must be structured, precise, balanced, and beautiful. This is why it is called Martial "ARTS". The respect to appear graceful while fighting is the discipline of the Martial Arts that makes techniques that seem ineffective, work in magical ways.
Sparring is a speed chess match while exhausted, frustrated, and under the pressure of getting our @$$ whipped! It is an ultimate game between 2 beings that conditions the mind and body to be superior in combat and self assurance. It is the safe, test firing range for the lethal empty hand weapons of humanity.
And THIS, ...is a "way" of the "Warrior's Edge"