Google’s PageSpeed Insights is an easy-to-use tool that tests whether a web page might be slower than it needs to be. It gives a score to quantify page performance. Because this score is concrete, the PageSpeed Insights score is often used as a measure of site performance. Similarly to PageRank years back, folks want to optimize this number just because it exists. In fact, Moz has a popular article on this subject: How to Achieve 100/100 with the Google Page Speed Test Tool.
For small sites on common CMSes (think WordPress), this can be accomplished. If that’s you, PageSpeed Insights is a great place to start. For most sites, a perfect score isn’t realistic. So where do we start?