With pertinent data now shown on the performance chart, advertisers can now better understand how minor changes impact their campaign performance. And per Google:
"For example, let's say you notice a drop in conversions for one of your active campaigns. With the change history report, you can now hover over the markers in the performance chart to get more details about the changes you've made over a defined period."
And great - advertisers can now use decision analysis to improve future campaigns more effectively, because any previous campaigns changes will show up on the chart.