By default, advertising on Facebook puts your ads first and foremost in the sidebar from a desktop view. Experienced marketers know that these ads are inferior to the news feed variations when it comes to click-thru and branding, so the old “best practice” of situating your images to work within a rectangle in the news feed and a square on the sidebar was ignored by most. Whatever it looked like in the sidebar was fine. The news feed was everything.
Now, Facebook is rolling out an update to the ads that kills two birds with one stone. First, it makes the sidebar ads more consistent with the news feed ads, meaning that the image used will look the same in the sidebar, only smaller. Second, it appears that the ads will be more prominent, making the potential for clicks higher than they were before.