How lazy loading works
By default a browser tries to fetch everything a page references, whether or not the visitor will ever scroll far enough to see it. On a long page with many pictures, that means competing downloads for content sitting well below the screen. Lazy loading changes the order: images and embeds further down are left alone until the visitor approaches them, at which point they are fetched.
Browsers now support this natively through a loading attribute on images and iframes, which needs no scripts and behaves predictably. Older implementations use JavaScript to watch the scroll position and swap a placeholder for the real file, which still appears in many themes and plugins. Video embeds deserve particular attention, because an embedded player often pulls in a large amount of third-party code before anyone presses play; deferring that until a click removes weight the visitor may never need.
Why lazy loading matters
The first screen is where a visitor decides whether to stay, and it competes for bandwidth with everything else the page has asked for. Removing that competition means the top of the page becomes usable sooner without deleting anything or making the page shorter.
The saving is largest exactly where it counts most: long service pages, blog articles, galleries and category listings, viewed on a phone. In Nepal, where most sessions are mobile and often on paid data, not downloading pictures the visitor never scrolls to is a courtesy as well as a speed gain. It also lightens your own bandwidth, since files are only served when they are genuinely wanted.
Common mistakes with lazy loading
The one that does real damage is lazy loading the top of the page. If the hero image or logo is deferred, the browser deliberately delays the very thing the visitor is waiting on, and the page measures worse than it did before the optimisation. Anything visible without scrolling should load eagerly.
Second, deferred images without reserved space make the layout jump. Each picture arriving pushes text down, and someone reading or about to tap a button loses their place. Stating width and height, or a fixed aspect ratio, keeps the space held open. Third, script-based approaches can hide content from crawlers that never scroll, so the image is effectively absent for search — a real risk for product photographs and for anything loaded through infinite scrolling, where the content further down may never be reachable by a link at all.
How to act on it
Use the browser’s native attribute where you can, and check what your theme or plugins are already doing before adding another layer; two systems deferring the same images is a familiar cause of pictures that never appear. Mark everything above the fold as eager, and let the rest default to deferred.
Always pair it with reserved dimensions so nothing shifts, and with sensible image compression, since delaying a heavy file only postpones the wait. Test by scrolling a real page on a phone rather than trusting a score, and confirm that important images still appear in Google’s rendered view of the page. If a listing relies on infinite scrolling, give it paginated links as well so both visitors and crawlers can reach everything. Lazy loading is one straightforward part of improving page speed, not a substitute for lighter pages.