Let me step back a bit and explain why this is incredibly important. In July 2007, Google released Message Center within Webmaster Tools. This gave Google a secure way to communicate accurate information and notifications to webmasters, in regards to their web site and how Google sees it. The only issue is that many webmasters did not bother registering with Google Webmaster Tools until after there was an issue with their sites. But Google did not, back then, have a message waiting for that webmaster – Google only provided future notifications to the webmaster.
With this new Google feature, a webmaster can notice a Google issue and afterwards register their site in Webmaster Tools to find past communication from Google on their site issues, if any. Many people are reactive by nature and not proactive, so this addresses the reactive type of webmaster.
On a security level, this is also very important. We have seen numerous reports of fake Google webmaster emails scaring webmasters into making unnecessary changes to their site because of a hoax or even worse. Webmasters should only trust communication from Google on site issues within the Google Webmaster Tools.
Even if you are not registered with Google Webmaster Tools, you can now see historical messages.