Sankey diagram is a very useful way to represent flow in a system. The flow happens between relatable entities and are represented by coloured links. The flow could be of any measurable quantity - material, cost, energy, etc, from one node (or entity) to another. It can be drawn in different layouts and gives a quick understanding of the flow balance in the system. Can use it to show energy flow in a system, or resource flow among members, or import/export among countries, etc. A sankey diagram very intuitively captures attention on the most important flow.

Learn more about Sankey diagram here.