Google PageSpeed tool was created to give webmasters an indiction of how their site will perform when analysed by the Google search engine. As Google takes a variety of different factors into consideration when ranking sites the tool gives an indication of the health of the site.
The score it calculated using a percentage, with different bounds of the score being coloured differently. Between 0 and 49 is poor and is coloured red, between 50 and 89 is average and is coloured orange, above 90 is considered good and is coloured green.
Getting a perfect score in the Google PageSpeed Insights tool is by no means the end goal of site performance improvements or even search engine optimisation. It will absolutely have some benefits in terms of your site traffic though and is worth including in your site key metrics.
Read more here: https://www.hashbangcode.com/article/drupal-9-getting-good-score-google-pagespeed-insights