Currently the lazy load intersection observer is set up using a rootMargin. This does not work well for pages that use images in CSS scrollers, like carousels, causing the images to load too late, when they become visible and the intersection with the root is detected. To work around this issue some developers are choosing to not use lazy loading, thus increasing the overall bandwidth usage for their sites. This problem was discussed in issue 431(https://github.com/w3c/IntersectionObserver/issues/431). Using scrollMargin for the lazy load intersection observer will allow lazy loading images to load when they are near the viewport as expected.
<rdar://problem/118706766>