[Kevin Sevcik]

Well, deadman switches aren't just a backup for E-Stops. They're often there specifically as enable switches for manual controls. So you have to active the switch before you can start moving around a large and dangerous robot, and you can't easily accidentally operate it.

Plus, how much use is an E-Stop button going to be if the machine you're operating electrocutes you, knocks you unconscious, or bores you to sleep? All of these situations leave the E-Stop button unpressed and the machine merrily humming away. Deadman switches don't just protect against machine operating dangers, they also protect against operator inattention.