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Largest Contentful Paint: how long until the main content appears. Interaction to Next Paint: how quickly the page responds when someone interacts. Cumulative Layout Shift: how much the page jumps about while loading.
Between them they approximate whether a page feels fast and stable rather than whether it technically loaded quickly.
The scores that count come from real users, aggregated over time. A laboratory test on a fast connection tells you about your test conditions.
That lag matters: after a fix, the field data takes weeks to reflect it. Teams frequently conclude a change did not work when it simply has not been measured yet.
Yes, modestly. Relevance matters considerably more.
Field data aggregates over weeks. It lags the deploy.
Usually images without reserved dimensions, injected content and late-swapping fonts.
Half an hour with your own data usually saves reading three of these. The guides will still be here afterwards.