Some objects, for example PriceBook Entry, must have their attributes set on insert as once created most of the record is not updatable, e.g. CurrencyISOCode cannot be changed on this record once it has been inserted. Providing a way to set these fields on creation, rather than a later update step, would allow these records to be deployed as currently PriceBook Entry records fail in multi-currency orgs as they are all created with the default currency causing SF to treat them as duplicates