User blog comment:Brandon Rhea/Ad Tests on Fandom/@comment-4627163-20170429220807/@comment-20644-20170430003309

This is a simplistic explanation, but page performance related to ad deals with what's known as "calls" in ads. There are a number of different functions that need to be "called" in every ad, such as displaying the content, using cookies, and more. All of these factor into page performance.

Let's say, as a conservative estimate, that there are 20 calls per ad and that there are 5 ads on a page. That's 100 calls. If we can use a featured wiki video that plays a video ad in front of it, that's another 20 calls. If we remove 2 ads from the page as a result, it removes 40 calls, leaving us with a total of 80. That may not seem like a dramatic drop, but it creates a meaningful difference in page performance.