Internal orders can be settled to various objects for cost monitoring and analysis. Two common settlement receivers for internal orders are Profit Centers (C) and Fixed Assets (D). Settling to a Profit Center allows the allocation of costs for internal reporting and performance measurement, while settling to a Fixed Asset is used for capitalization of costs associated with the construction or acquisition of assets.
Reference = SAP S/4HANA Financial Accounting (FI) and Controlling (CO) configuration guides and help documentation.