Bullet Punch deals around ~60% to Salamence, add Stealth Rock damage, plus Life Orb recoil, that is almost a OHKO. It Pursuits Latias, and takes around ~50% from a Specs Draco Meteor, which lower her SpA by two stages so she can definitely not KO me. Bullet Punch helps a bit more against Dragonite some.
Well, one kill helps a lot, and killing a key member can open a sweep. Usually I save my Pokemon till later on.