Compare to the default Use Google+ Comments in Blogger commenting system, Google plus commenting system gives you more power to go social and will help you to build a better community around your BlogSpot blog. If you have a blogger enabled blog, you should consider enabling Google plus comment system on your blog. One of the biggest benefits of using social commenting system is fewer spam comments. Now, click on Switch now, and your Use Google+ Comments in Blogger blog has linked to your Google plus profile. On the next page, you can select the box to add the blog in your profile, which you should do, if you wish to take advantage of Google authorship (Profile picture in Google search)
Use Google+ Comments in Blogger
Overall, Google plus commenting system has more pros than the cons. The tough decision is for old bloggers who are blogging on Use Google+ Comments in Blogger platform for long and using 3rd party commenting system. From the future perspective, Google plus commenting system is good and have many advantages for your blog, but if you are considering to switch to WordPress in near future, you might not want to use Google + comments in blogger.
I would like to add one more point here. You will lose the comments tab on blogger dashboard if you once enable Use Google+ Comments in Blogger. But you can still moderate comments within the blog post itself by clicking on the drop-down arrow next to the comment, or by hovering over the comment and clicking the “Use Google+ Comments in Blogger” that appears.