. With annotations, you can direct people through links to videos, and you have to go to each individual one to create them. With this feature, you can push a video of your liking across every single video you have in your catalog. It places a thumbnail of the featured video into the corner of every video so that no matter which one a viewer is watching, it's there, ready to be clicked. You get to push a video that you think either represents your best, or you can push one you don't think got the attention it deserved. Now, it's way more dynamic than having a little text link show up. Hopefully, they'll make this more customizable in the future so that you can feature a number of different videos across different areas of your catalog. But for now, this is a nifty feature.
Full article: http://www.reelseo.com/youtube-invideo-programming/