A robot near people needs more than ordinary software to stop it in an emergency, because ordinary code can fail silently. Safety-rated stopping uses certified, independent mechanisms that reliably bring a robot to rest when a guard is triggered or a person enters a protected zone.
Crucially, some such stops hold the robot still without cutting all power, so it can resume smoothly rather than needing a full restart. These functions are tested to defined standards precisely because a safety feature that merely usually works is not a safety feature at all.