Why does site speed matter?
Google uses page experience (Core Web Vitals) as a ranking signal; slow mobile sites lose both rankings and customers. A large share of visitors leave a page that does not load within a few seconds.
What do the scores mean?
90–100: good · 50–89: needs work · 0–49: poor.
LCP is when the main content appears (under 2.5 s is good), CLS is how much things shift while loading (under 0.1 is good), TBT is how long the page is blocked from responding (under 200 ms is good).
Low score — where to look first?
The usual suspects: large uncompressed images, unnecessary plugins and scripts, a slow server, late-loading fonts and ad/analytics code. Sites built on off-the-shelf themes tend to have all of them at once.