You might want to create “what if” scenarios in your dashboards, where you can see how a change in a particular value will affect other metrics. For example, you might want a dashboard that shows values converted from one currency to another, and allows the user to adjust the exchange rate and see how that affects revenue.  

Calculation variables allow you to define these values. You can then build calculated metrics that are dependent on them. 

The video below walks you through an example of creating an exchange rate calculation variable, applying it to a metric and building a dashboard that uses both.