User blog comment:Brandon Rhea/Intro to Wiki Modernization/@comment-25356303-20170306205842/@comment-20644-20170307003009

For each ad, in addition to calling the image and sometimes more markup for more complicated ads, you have to make a whole bunch of calls. Each of these calls allows a website and advertisers to do common things, like targeting specific demographics. So if we're being conservative here and said that, for each ad, 20 calls were required and you have 5 ads per page, that's 100 calls per page. Contrast that with just having one video ad with 20 calls and a smaller number of other ads, and it could make a meaningful difference.

Regardless of how many ads end up being on the page, the aim is to have the overall number of calls we have to make on each page go down. We strongly believe that if we do this, we can get the page to load faster.