Google+ comment system is an alternative to blogger default comment system which is available to only bloggers with profiles upgraded to Google+.
The following are what you can see when you've enabled the Google+ comment system on your blogger blog.
*. Comments made on your Blogger blog post
*. Comments on the blog post that you’ve shared to Google+
*. Shared content on Google+ that links to your blog post
Readers will need a Google+ page or profile to comment on your blog.
*. It is also a good way to wipe out spammers as only users with Google+ profiles can comment on your blog.
Features Of Google+ Comment on Blogger
Google+ Comments look similar to traditional Blogger comments, but have some important differences. For example:
*. When you leave a comment on a blog, you'll see the option, checked by default, to also share that comment to Google+.
*. Google+ posts that link to blog posts will show up as a comment underneath those blog posts
*. If original comment is shared to Google+, replies to the comment on the blog will show up in Google+ and vice versa, but only to the people that the original comment was shared with
*. If a comment is not shared with the blog author, the blog author will not be able to see the comment in either location
*. As the author of a post, you’ll receive Google+ notifications when readers comment on or share your blog post.
How To Enable Google+ comment on Blogger
1. Sign in to Blogger
2. Click on the “Google+” tab in your blog’s Dashboard
3. Upgrade to Google+ if you haven’t already done so
4. Enable Google+ Comments. Comments already made on your posts will keep working in the new widget