The sizing keys used in the Salesforce B2B Commerce Global APIs perform five distinct operations. Three of these operations are:
Refetch data (used on some Logic classes): This operation indicates that the data should be refetched from the database instead of using the cached data. For example, ccrz.ccServiceCart.getCart(ccrz.ccAPI.SZ_REFETCH) will refetch the cart data and refresh the cache.
Related Query to call (sub queries or direct queries): This operation indicates that the related entities should be retrieved by using sub queries or direct queries. For example, ccrz.ccServiceProduct.getProducts(ccrz.ccAPI.SZ_SUBQUERY) will use sub queries to fetch the related entities for each product, while ccrz.ccServiceProduct.getProducts(ccrz.ccAPI.SZ_DIRECTQUERY) will use direct queries to fetch the related entities separately.
Object type casting: This operation indicates that the data should be cast to a specific object type. For example, ccrz.ccServiceProduct.getProducts(ccrz.ccAPI.SZ_SOBJECT) will cast the data to sObjects instead of transformed objects. Salesforce Reference: B2B Commerce and D2C Commerce Developer Guide, Data Sizing Conventions