[WnZ39p0Dgydaz1]

Instead of a Markdown file, imagine your data is somewhere in a REST API, or many REST APIs. Gatsby (and next.js, which I vastly prefer) will query these APIs during the BUILD process to generate your static sites - and that can be slow. Imagine you have a site that list the top 1000 IMDB movies with details. To generate your static site, you need to make 1,000 REST calls to the IMDB API during build time to get the necessary data. Parallelizing and caching it makes it faster.

If it were just Markdown files you probably wouldn't need this since parsing and transforming local Markdown files it fast. But this is Javascript, so nothing is truly fast.