Tridion Docs 15.1 will have Metrics feature that will have a set of predefined charts:

- Content reuse chart will show you the reuse level for a selected period highlighting the amount of new content compared to the one that was reused and the reuse level

- Return on Investment chart shows the value of using Tridion Docs for a selected period based on the customer’s reuse level versus creating content from scratch. As well as showing a trend over a specified period to see how much you are saving with Tridion Docs

- Productivity chart shows publishing activity for a selected period indicating the status of published outputs

There is also a recent blog on community explaining the reuse formula:  A guide how to understand Tridion Docs’ new Reuse Metrics