The time taking for loading a website is also an important factor of its seo. Google mostly like less loading time sites it is because if a site take 10 seconds to load when a visitor came into the site and found that the site take more loading time so that sometimes in a possibilities that he waits for it otherwise he quit it and look in other sites. One of the measurements of seo score is depend on the loading time, the main reason for more loading is because of the graphical rich of the site, it is necessary to avoid maximum images and ads in the homepage because the loading time of a site is determined according to the loading time of the homepage. So pop under ad networks are somewhat a harmful thing to the site and also google never likes this kind of ads on the sites because it take more loading time. A site need to contain a good graphical designing but need to reduce maximum graphic richness. The best way to reduce the loading time is avoid images, banner ads etc in the homepage. Most of the ad networks suggest their publishers to place less than 3 ads in a page, the two reason behind it is one can reduce the loading time of the page so the visitors came to the site without passiontely and second is the avoid more impressions.
Text ads are the best ad thing which is suited for a homepage because it is not much graphical rich as the banner ads. Contents are the key of a site, if a content contains images to explain the content information then in order to reduce the loading time only place 1 or 2 ads in that page otherwise it took more loading time than the other pages because of its graphical richness.
Loading time has an important role in the development and increasing seo stats of a site so use the graphical images and ads in the way of it is needed. This is upto the seo skill of the webmaster. All the best.