Performance is a design problem. A slow product is a bad user experience. A bad user experience loses users. Framing performance this way — rather than as a purely engineering concern — changes which conversations designers get invited into and what gets prioritized.
The Business Numbers
Amazon found that a 100ms increase in page load time cost 1% in revenue. Google found that mobile pages that load in under 5 seconds have 70% longer sessions. Walmart found a 1-second improvement in page load time corresponded with a 2% increase in conversions. These are not edge cases — they're consistent findings across industries.
Core Web Vitals as Design Metrics
Google's Core Web Vitals measure: Largest Contentful Paint (how long until the main content appears), Interaction to Next Paint (how quickly the page responds to user interaction), and Cumulative Layout Shift (how much the page jumps around as it loads). All three are design-relevant. LCP is affected by image optimization and loading priority decisions. CLS is caused by images without dimensions, fonts that swap after load, and dynamically injected content.
The Designer's Performance Budget
Every design decision has a performance cost: images, fonts, animations, third-party widgets. Designers who don't consider this cost externalize it onto engineers, who then have to make trade-offs without design input. Working within a performance budget — a maximum page weight, a maximum number of network requests — produces designs that are feasible to build quickly.