Why Sankey? - AndreasHeese/4sg GitHub Wiki

If numbers are not simply written in a table, but presented as a graphic, connections become clear and trends get visible that could be missed. That's why Spreadsheets offer the option of creating charts of lines, bars, pies and so on.

One diagram type has not yet been conquered by Excel: the Sankey diagram. It only suits special tasks, but for them it's perfect. If you want to stick with Excel for this, you have to rely on third-party tools. On the net using "SmartArt" is also suggested, but that can't visualize actual data.

What is a Sankey diagram? Wikipedia explains it this way:

Sankey diagrams are a type of flow diagram in which the width of the arrows is proportional to the flow rate.

Sankey diagrams emphasize the major transfers or flows within a system. They help locate the most important contributions to a flow.

Sankey diagrams are named after Irish Captain Matthew Henry Phineas Riall Sankey, who used this type of diagram in 1898 in a classic figure […] showing the energy efficiency of a steam engine.

Sankey diagrams are more about what route does data go rather than how it changes over time. In it's field, it can be enlightening about tricky data.