If you think of all the things that Google can measure in terms of performance, accessibility, SEO, best practices, problems, errors or anything else like that, Dev tools can present that information to you. Imagine the complexity of all that information and they just go you know what that’s too complex let’s bubble up scores to some peaks and figure out might make good sense for measuring user experience using these peak scores.

They’ve also come up with these nicknames like cumulative layout shift and first input delay, so you have all of these kinds of things that are sort of like a goal of several metrics underneath so that those metrics underneath calculate up to that goal and things that can get in the way of something like first input delay for example, are render blocking resource downloads or scripts that take a long time to evaluate.