When you run a template and it is using way too much data, generating a gigantic report, this makes it easy to discover why. This tool provides a quick summation of the number of rows of data each forEach tag in the template will return. And it provides how much time it took for the datasource to return that data.
This provides a quick verification that the amount of data returned is what is expected. It also quickly shows which queries are pulling down more data than you expected.