If you're using the Financial Reporter or Sage Intelligence for reporting AND you wish to view budget vs actuals, then it is extremely useful (required) to enter your budgets into Sage 300.
*Note: Budgets can be imported from a spreadsheet

What Shane said.  Check the documentation out for Budgeting by starting at page 51 of the G/L User Guide.  You can import budgets, or create budgets based on a rule (percentage, fixed amount, etc) + prior year Actuals, and best of all you have multiple budget sets so you can do forecasting based on different scenarios.