Glossary
What is Lazy loading ads?
Also called: lazy load, lazy-loaded ads
Lazy loading requests an ad only when its slot gets close to the screen, instead of loading every ad on the page as soon as the page opens.
हिंदी में पढ़ेंWithout lazy loading, every ad on a page is requested as soon as the page loads, including slots that many readers never reach. Those ads still load, slow the page and pull viewability down. Google’s Publisher Ads Audits flag pages that load more than three ads below the fold.
In the Google Publisher Tag you set two margins as percentages of the viewport, the visible screen. fetchMarginPercent sets how far away an ad is requested, and renderMarginPercent how far away it is drawn; 100 means one screen away. mobileScaling multiplies both on phones. The older enableLazyLoad() call is deprecated in favour of the lazyLoad setting in googletag.setConfig().
The real risk is a margin that is too tight. If your auction takes one second and a reader scrolls past faster than that, the slot arrives empty and the impression is lost. Phones scroll faster, so widen margins there, and compare viewable impressions per page view before and after.
Example
An article has 5 ad slots and half its readers never reach slot 5. Over 10,000 page views, loading everything requests 10,000 ads for slot 5, of which 5,000 can never be seen. With lazy loading, slot 5 is requested only for the roughly 5,000 readers who scroll near it.
Why it matters to publishers
Lazy loading cuts wasted requests, speeds up pages and tends to lift viewability. Set the margins too tight, though, and you lose impressions that would have been seen.