It's easy to test a site on office fibre, get a near-perfect Lighthouse score, and call performance done. Then a client in a secondary city mentions the site feels slow on their phone, and the gap between tested performance and real performance suddenly isn't theoretical anymore.
A CDN helps — it just doesn't fix the last mile
A CDN gets your files physically closer to the visitor, and that genuinely helps. But if the connection between someone's phone and the nearest edge node is still a congested 3G or throttled 4G link, the CDN's job is basically done — the actual bottleneck is that last stretch, and no amount of edge caching reaches it. What moves the needle there is sending fewer bytes in the first place.
Where the weight actually comes from
Images are usually the biggest single offender. We serve modern formats — WebP or AVIF — with explicit width and height so nothing shifts around while it loads, and we lazy-load anything below the fold so the first paint isn't held hostage by images a visitor might never scroll to. On one e-commerce rebuild, this alone cut the initial page weight dramatically without touching a single pixel of the design.
JavaScript is the second lever, and it's sneakier. Every third-party script — a chat widget, an analytics tag, a marketing pixel — adds parsing and execution time on a low-end device, even after the network request itself has finished. We audit these on every project and cut whatever isn't earning its cost, deferring the rest until after the main content is already interactive.
Fonts are a smaller cost but a real one. Self-hosting them, instead of pulling from a third-party font CDN, removes an extra DNS lookup and connection before a single character can render. Pairing that with `font-display: swap` means text shows up immediately in a fallback font rather than staying invisible while the real one downloads.
None of this is exotic. It's mostly discipline about what gets added to a page and when it's allowed to load — but that discipline is the actual difference between a site that scores well in a lab test and one that feels fast to someone on a real 3G connection outside the main metros, which is a large and easy-to-forget slice of who's actually visiting.