lightbulb_outline Blog Post: Fast ads matter (web.dev)

Avoid loading ads until they are nearly on-screen

Overview

This audit ensures that no more than three ads are loaded outside the viewport. Ads outside of the viewport are less likely to be seen by users, so loading an excessive number of them can lower viewability rates and decrease page performance.

Recommendations

Defer loading ads outside of the viewport until they are nearly on-screen. See the Google Publisher Tag Lazy Loading API for an example.

More information

GPT Reference
Viewability best practices