It allows you to connect your blog to your Google+ page, notify followers when you publish, and let them recommend your content.
Here’s how it works, according to Blogger: Every time you post, Blogger will show a Google+ share box to let you notify your followers that you have a new blog post.
The process is semi-automatic, but it enables you to save time as you don’t have to go the blog post to click the Google+ button.
To get started, click the “Google+” tab in the Blogger dashboard and then the “Upgrade” button. If you’ve already upgraded to Google+, Blogger will help you associate your blog with your profile or page.