As per D. McGreal and R. Jochan in their book The Professional Product Owner, the Usage Index determines how a product and its features are difficult to use, difficult to find in a messy User Interface, or if we are maintaining costly software which nobody cares about.

The functionalities at the bottom of the chart might be features for the admin users, or our biggest bet a few releases ago. We expected it to be a “killer” functionality, but it looks irrelevant for most users. Should we invest more in users’ training or highlight that menu option in the main page of our application? It might be worthy, but please make sure you have not fallen prey to the Sunk Cost fallacy. After a few attempts, maybe it’s time to remove that code from our code base.

According to the Chaos Standish report, as mentioned in the book, even this follows a kind of Pareto principle: only 20% of production functionalities are used often, meanwhile a sound 50% is hardly ever used.