Why image size affects speed and SEO
Images are often the heaviest part of a page. Oversized images slow loading, especially on mobile networks, and affect Largest Contentful Paint (LCP), one of the Core Web Vitals metrics Google looks at.
The two most effective steps: match the image width to the size it is displayed at (don’t upload a 4,000-pixel photo for an 800-pixel slot), then compress at a quality of 70–85, which is usually hard to tell apart from the original.