The common mistake is uploading huge original photos and letting the browser shrink them, which still downloads the full file. Serving an image at the size it appears, in an efficient format, can cut its weight by 70% or more with no visible quality loss.
Modern formats (WebP, AVIF) pack the same quality into much smaller files than older JPEG or PNG. Combined with lazy loading and reserved dimensions to prevent layout shift, proper image handling improves LCP, CLS, and total page weight at once.
Updated July 2026