The butterfly slide is probably the most used save in the NHL today. It's so common because you cover the complete lower part of the ice and if out far enough you can have the whole net covered. When balanced and in control it is very easy to make saves from the butterfly slide.
When doing the butterfly slide there are a couple of things that should be remembered. First you want to load your push leg by crouching down for lots of power on your push. Next you want to look where you are going and make an explosive push across the net. Keep your stick on the ice and your glove and blocker up and out so that you are ready to catch anything or block anything. Make sure that your legs are flat on the ice and keep your body compact so that no pucks can slip through you. Always have a wide butterfly so that you get maximum lower net coverage.