The Contacts share Store Credits parameter is used to enable the Contacts share Store Credits function.
The Configuration Manager, Settings, Databases "Contacts share Store Credits" setting is enabled (turned ON) by default meaning Store Credits are saved by Customer Number only and all Contacts attached to that Customer can use or add to the Customer's Store Credit balance. If it is disabled (turned OFF), Store Credits are saved with the Contact ID and are identified using the Customer Number and the Contact ID. Only the specific Contact can use or add to their own Store Credit balance. (Customers without Contacts always use the blank Contact ID).
See:
Edit Store Credits
Configuration Manager Contents