If Samus siphons energy from something, she gains health, and if she gives energy, she loses health. Giving up energy is a useful gameplay mechanic - Phazon enemies can be overloaded and explode, and later into the game, Samus is practically required to lose energy via this method. The Grapple Voltage can also be used to drain energy from certain enemies (like Shield Pirate Troopers or "Dragoon" Battle Drones) which can be grappled. In some cases Samus needs to drain energy into special terminals to power down shields blocking doors.