If you are setting up projects you can use both or either the forecasts or budgets. They have differing amounts of details that you can use for different purposes through the management of the project. If you have created forecasts then you can copy them to a budget as the foundation for the budget.
Here is a quick overview.
AX2012 R3 Cu11.
Pingback: Create a project budget from a forecast - OrganicAX - Dynamics AX Users - DUG·
Pingback: Create a project budget without a forecast | OrganicAX·
Pingback: Create a project budget without a forecast - OrganicAX - Microsoft Dynamics AX - Dynamics AX Users - DUG·