Cost Allocations allow you to allocate budgets, holds, contracts, schedule items, and change orders to sub-projects called components using percentage-based allocation rules. Components are sub-projects that you can allocate and track costs with. Budgets, holds, contracts, schedule items, and change orders can all be assigned to components based on the percentage-based logic of the allocation rules tagged to them. See What are Cost Allocations and Components in Portfolio Financials? for more information.
You can enable Cost Allocations when adding a new Portfolio Financials project, or by changing the settings on an existing project.