The 4 MB hero image
One uncompressed photo, straight off the camera, loading before anything else on the page.
Placeholder content — replace before launch.
The symptom
The largest image on the homepage is several megabytes and 6000 px wide, displayed at 1200.
Why it matters
It is usually the Largest Contentful Paint element, so it sets the number a visitor experiences as “how fast the site is”.
How to check
DevTools → Network → Img, sorted by size.
How to fix
Resize to the largest size actually displayed, export as WebP or AVIF.
When it’s actually fine
A photography portfolio has a real reason to serve large images. Serving them lazily, below the fold, is a different situation entirely.