This article provides detailed explanations of the cost dashboards available in PPO:
Cost S-Curve
The S-Curve is an important but often overlooked and misunderstood project management tool. The Costs S-Curve is appropriate for projects that contain labour and non-labour tasks. It shows cumulative costs expended over time for the duration of the project, and is used to assist in the calculation of the project's cash flow, and cost to complete.
Please note that this dashboard can only be used on PPO instances that have month and year parameter on the cost entity as required fields.

Costs Dashboard
The Costs Dashboard is a graphical representation of the total budget, spent and other relevant key statistics for the costs across all the projects. The two graphs on the dashboard change, based on the “Group By” fields selected on the dashboard criteria. In the example below we have grouped by Cost Estimate and Month (which is the second group by field on the cost dashboard).
The Costs Dashboard combines the information, by using the report criteria, to show three sections on the dashboard.
The bottom graph shows the cost budget vs actual spent, grouped by Month.