I'm going to try to throw out a serious answer, so maybe this thread can die. Why are lats important?
#1, Punching power relies on transferring force and momentum from the ground through your body and into your target, and the powerful muscles of your upper back are vital to this process: they're part of the "chain" of force transfer.
#2, Even if you were just throwing "arm punches" without good technique, muscle antagonists are necessary for power...your body generally doesn't "let" you throw a punch so hard that you can't stop it, as this would cause injury, so the strength of "pulling" muscles affects striking power.
#3, The most obvious reason, grappling requires pulling muscles more than pushing. Breaking your opponent's posture, throwing them, or holding an armbar are good examples of lats being used.