I think the CB shunt is used for remote tripping , it is used on low voltage panel especially if there two source feed one load ( primary source and standby source ).
Shunt trips can be used for remote tripping or allow another protection element to trip the breaker. For example, an LSIG MCCB will inherently provide phase and ground overcurrent protection but an external 27/47 to a shunt trip can add undervoltage/phase balance elements to the breaker.