Comparing new customers with old customers or numbers after an event could be a great way to gleam insights of your metrics.
For this to be a success, make sure you have Historical data.
Reference
Ries, Eric. The Lean Startup: How Today’s Entrepreneurs Use Continuous Innovation to Create Radically Successful Businesses. 1st ed, Crown Business, 2011.
Highlights or timestamps
By comparing cohorts, in this case groups of users who signed up at different times, and their respective recommendation rates, you can see whether you’re advancing towards your goal.
— ^4e2efc from The Lean Startup
When analyzing data, it can be helpful to use the so-called cohort analysis. Instead of simply looking at how the revenues or user base have grown in general, compare how new customers behave compared to old ones.
— ^298820 from The Lean Startup