Gatsby 4 introduced Deferred Static Generation (DSG) alongside Static Site Generation (SSG) and Server-Side Rendering (SSR), allowing pages to be generated upon user request and then cached for subsequent visits, thereby improving build speeds for sites with numerous pages receiving varying levels of traffic. This tutorial by Lennart Jörgens demonstrates how to use analytics tools like Google Analytics or Plausible to determine which pages to defer based on their popularity, using APIs to automate this process. It guides users through setting up a local plugin for gathering analytics data, creating GraphQL nodes, and configuring Gatsby to defer less-visited pages while maintaining SSG benefits for high-traffic pages. The process involves setting up an analytics tool, deploying the site to Gatsby Cloud, and leveraging Gatsby's GraphQL data layer to inform page generation strategies. This method allows for a granular approach to page deferral, enhancing site performance by only building frequently visited pages as SSG and marking others for DSG, thus optimizing the site's speed and reliability.