Why we used field data instead of lab data to guide our Core Web Vitals improvements

There is a good description of what lab data and field data are here.

1. Changes in lab data was not reflecting what we were seeing on pagespeedinsights field data or in the Chrome User Experience monthly report.
2. Lab data only covered the first page load but CLS (Cumulative Layout Shift) continues accumulating as a person scrolls through a page.

Field data collection setup takes effort and time but we have found it is worth the investment.