The target here is to cover as much net as possible, all the way to the opposite post. A perfect Butterfly slide requires strong leg power to drive the goal tender across the crease and eliminate the open net, it also requires a tightness in the 5 hole, good stick position, and good pad extension.
Leg recovery off the save is essential. When in the Butterfly position, you must push in the opposite direction and follow the puck in tight (creating a wall down low).
All great goalies have the ability to use this save to keep the puck out, and keep their team in the game.