Let’s be honest: YouTube has some of the best and worst (mostly worst) comments on the internet. In order to rectify that glaring issue for a site that gets a billion views monthly, Google has made a simple one-touch button that will link your Google+ account with that of YouTube.
This way, you can comment with your real name, and this allows for more clarity, a bit less spam, and overall a better experience — theoretically.
Things will always be topsy-turvy on YouTube, but this is a stage of resolving that.
Via: Google Blog