Google Adsense had just implemented personal inbox into publishers account. From now onwards, Google Adsense will be sending you customized optimization tips. According to Arlene of Adsense Publisher support, these tips could varies from publisher to publisher, you will be receiving tips that suites you but not others.

our system will automatically analyze your account and ad settings. Based on these findings, you’ll receive a notification each month in your AdSense account if there are changes you can make to improve your overall AdSense performance.

This is something really thoughtful of Adsense. IMO, if it’s a optimization tips from the house itself it won’t go wrong.