Purpose drives requirements. The shape of a cost model must fit its intended uses.   MORE....

• Budget: An Investment-based Budget uses a cost model to present a budget that forecasts the costs of what the organization wants to sell, not just what it wants to spend.

• Rates: Unit costs are used for chargebacks, allocations, project estimation, and external benchmarking. They're based on plans (future costs), not historic accounting data.

• Profitability analysis: Analysis of product-line profitability requires a cost model based on historic data, not plans.