Lazy loading

Lazy loading waits until an ad slot is about to enter the screen before it fires the ad request. Ads at the bottom of a long article only load if the reader actually scrolls that far.

The benefits are faster pages, less data used and higher viewability, because ads are only served when they have a real chance of being seen. Buyers pay more for viewable impressions, so lazy loading can raise eCPM even though total impressions drop. Google Ad Manager and Prebid support lazy loading, and publishers tune the trigger distance (for example, load when the slot is one screen away).

The trade-offs are fewer total impressions and a risk of blank ad slots if the ad loads too late for fast scrollers. Aggressive infinite-scroll designs that combine lazy loading with endless new slots can also inflate inventory and resemble made-for-advertising sites layouts.

Think of it like this

Lazy loading is like a waiter bringing each course only when you have finished the last, instead of piling every dish on the table at once.

An example

After enabling lazy loading, a news site's impressions per page fall from 8 to 5, but viewability rises from 45% to 72% and revenue per page rises 10%.