Site speed usually enters the conversation as a search ranking factor, which understates it. Search engines apply a modest adjustment. Customers apply an absolute one: they leave.
Where the time actually goes
In our experience the same handful of causes account for most of it. Images exported at full resolution and scaled down in the browser. Fonts that block rendering while they download. A tag manager container with years of accumulated scripts nobody has audited. A page builder that ships the styles for every module whether the page uses it or not. Third party widgets, each loading its own framework.
Caching is not a speed strategy
A caching plugin hides the symptom on repeat visits. It does very little for the first time visitor arriving from search or an ad, which is exactly the person whose experience you are paying for.
Fix it at build time
Responsive images in modern formats, generated automatically. Fonts subset, preloaded and served with a sensible fallback so text is readable while they arrive. Scripts deferred, third parties loaded on interaction rather than on page load, and a hard budget on total page weight that the build is not allowed to exceed.
Measure what people experience
Lab tools are useful for diagnosis but they run on a synthetic connection. Field data, such as the Core Web Vitals report in Search Console, tells you what your actual audience got on their actual devices and networks. That is the number worth reporting.
The honest framing
Speed work rarely produces a dramatic chart on its own. What it does is stop quietly losing a slice of every acquisition channel you pay for. It is maintenance rather than a campaign, and it is close to the cheapest conversion work available to most sites.