Reading and responding to comments can be one of the most rewarding aspects of blogging. Not only do they help you connect with your readers, they can also inspire later blog entries. The challenge, oftentimes, is following all the conversations around your content—on Google+, for instance, as well as on your website. So we're making things a lot simpler.
Starting today, you can bring Google+ Comments to your Blogger blog. Once you've enabled the feature through your Blogger Dashboard, you'll enjoy a number of important benefits: Yonatan Zunger
Actually only two. And with those come some big downsides: only people with Google+ profiles can comment, which can severely reduce your interaction with readers, and you loose the ability to moderate and export comments from Blogger – since they are actually Google+ posts, moderation must take place on Google+.
I’m not sure if I remember correctly, but when Facebook Comments launched, they added support for third-party logins pretty quickly. I am pretty sure Google has no plans for a similar move – and as such I’m not going to use this new system anytime soon. As it stands now it’s just another weak attempt to grow Google+ on the back of a service that people actually use.