A Content Delivery Network (aka “CDN”) provides an optimized way to deliver content (HTML responses) to your end users. The CDN accomplished this by caching your files on servers around the world, which reduces the network distance for the end user to download the file.
Typical uses for a CDN is to make web browsing faster by service all static files via the CDN. This reduces the load on your web server host as well as reducing the time it takes for individual users to retrieve those files. Your website will load faster if your CSS, JS, font and image files are served via a high-quality CDN. It does take a bit of extra work to get a CDN up and running, so this is something that you will typically do once you have a large user base, and especially if you have users from around the world accessing your site.