PocketWizard 804-513 N90M3-P Nikon Pre-Releaseable Motor Drive Cord Works with all models of Pocket Wizards In simple terms it "wakes up" the camera. In most newer electronic cameras the meters and auto-focus systems do not operate until you press the shutter release button down halfway. PreReleasing keeps the camera "awake" all the time which is the same as continually holding the camera's shutter release button down halfway.