This unit will appear the end of your sidebar. As the user scrolls past the end of the sidebar and there’s content to continue reading, it will stick to the top of the screen.
The key to this unit’s performance is as short of a sidebar as possible, so that as they user scrolls down through your content, the unit stays with them for a good long while. This leads to higher viewability, which leads to much higher CPMs.
Since it is lazy loaded, it will not load until a user scrolls near it.
Again, the way to maximize this ad is to have it load soon on the page, and scroll with the user a long time.
That means shorter sidebar + longer content = more money for you. Keep that in mind as you write new posts, and reformat your older, most popular ones.