When fired at a star, a supernova explosion would be triggered, destroying everything in its path. The Resonance Torpedo Launcher was the only superweapon capable of destroying an entire star system and killing trillions of sentients at one time.
During the Death Star's development, the Resonance Torpedo Launcher was a proposed weapons system for the battle station.
The same technology used in the Resonance Torpedo Launcher was later used in the Sun Crusher, and the Eclipse.