Sankey chart shows the flow and the relationships between two different elements
Sankey chart is a visualization method for adding a specific type of flow chart to the sheet you're editing. In the Sankey chart, the width of the arrows is displayed proportionally to the flow quantity.
This type of chart is great to visualize the transfer of energy, materials, money, or any system process. Flow lines or arrows can be split or combined together through their paths on process stages.
The width of the lines or arrows is usually an indication of the magnitude. That being said, the bigger the arrow, the larger is the quantity of the flow. Coloring is used to categorize the flows or processes.
The Sankey chart is valuable when you need to find the most critical areas of overall flow. The diagram is also very helpful when you need to display explicit quantities maintained inside system boundaries.