Those who analyze how AdSense ad units or channels perform compared to each other to decide whether you should make changes to improve performance. In the new AdSense interface the "chart" feature allow you to see custom channels or ad units as their own line on the graph, so you can easily identify spikes or dips.
"To see how your channels perform compared to each other, visit the Performance Reports tab, and click Custom channels. Depending on the number of channels you're using, you might be asked to filter the list and then click Update report. Once your selected channels are listed below the graph, you'll see the Combine and Chart buttons.
Select a few channels and hit "Chart." Now you can see each specific channel in it's own color on the graph. You can use the buttons next to the graph to change the metric for which you're comparing the channels," explains Google.
Using this feature, you might notice that discrepancies between channel performance are more obvious on the graph than they are just viewing the numbers in the table.
[Source: AdSense blog]