Images typically account for 50-70% of total page weight on landing pages. A hero image exported from Figma at 2x resolution might be 2-4MB. Serve that to a mobile visitor on 4G and you've just added 3+ seconds to your load time. Image optimization is almost always the single highest-ROI performance fix available.
The modern stack: serve WebP (30% smaller than JPEG at comparable quality) with AVIF as a progressive enhancement (50% smaller). Use the <picture> element with srcset to serve different sizes for different viewports — a 400px-wide phone doesn't need a 2400px image. Compress aggressively: most hero images look fine at quality 75-80.
The mistakes I see constantly
Serving a 3000x2000 PNG hero image because "the designer wanted lossless quality." Your visitors can't perceive the difference between an 85-quality WebP and a lossless PNG on their laptop screen — but they absolutely perceive the 4-second load time difference. Also: logos and icons served as PNGs instead of SVGs, decorative images not lazy-loaded, and the same massive image served to mobile and desktop viewports.
Run your landing page through Lighthouse and look at the "Properly size images" and "Serve images in next-gen formats" audits. If you see potential savings there, you can probably cut your page weight in half in an afternoon. That directly translates to faster LCP and better conversion rates.