Manual motor starters are electromechanical protection devices for the main circuit. They are used mainly to switch motors manually ON/OFF and protect them fuse less against short circuit and loss-phase.
None-fuss protection with a manual motor starter saves costs, space and ensures a quick reaction under short-circuit condition, by switching off the motor within milliseconds.
Manual motor starter combinations are setup together with contactors and overload relays.
Industrial version here: Motor protective circuit breakers Ex9S32A