The Revenue Breakdown tab allows you to mark some significant events for your business so you have a reminder why the numbers are such. 

Let’s say that you make a redesign of the your checkout process and you want to measure how the change affects the revenue generated.  You can easily do that by clicking on the plus below the date of the significant event and type in your note, describing the change.

The mark will stay in the interface as an orange dot, which you can always check for reference.