With the Shipment Date Code Handling parameter you determine whether and how you want to run TRIMIT Collection Management with sales. This is often set up in an Order Type but if the Shipment Date Code Handling of the Order Type is set to Based on Setup or if you do not use Order Type, the setting of this parameter will be valid.
Follow the link to the Shipment Date Code Handling of the Order Type to read more about the functionality of this parameter.