The Budget Options  selection criteria can be used to indicate which type of budget (or plan) information should be included in the output.  

• Budgets can be calculated from project budgets, task budgets, people/expense plans, or people/expense assignments.
• All budgets (project, task, plans, assignments) will be allocated.  Meaning that the budget will be spread across the items data range and only the part of it that overlaps the report's date range will be included.
• People and expense assignments are also subject to "enforce WBS dates" restriction.  If the project enforces WBS dates, the project's range must overlap the reporting range and the project must not be completed before the report's start.  If either of those conditions is not met, none of the assignments will be included.  Additionally, the same restrictions apply to the tasks and task-level assignments.