A better signal-to-noise ratio and more interaction with people you care about
Just as was promised back in September, YouTube is getting a new comment system based on Google+ with several new features. The new system will surface comments from people whose comments you care about most, such as your Google+ friends, the video maker, engaged commenters and other well-known YouTube personalities. Of course if you still want to see the flood of comments roll in, you can switch to "newest first" from "top comments."
One of the biggest bonuses in moving to Google+ for YouTube comments is being able to have a mix of private and public discussions on a single video. You can limit your comments to just specific circles or specific people, right alongside your public comments that everyone can see on the page.
A likely best of all if you're a YouTube video creator, you now have even better ways to moderate comments on your videos. You can review comments before they're made public, block certain words or auto-approve comments from specific people.
Source: YouTube Blog