Worker Sites basically adds a subfolder to your project containing a Worker script that gets deployed to your domain and serves up your build output.

It's lower-level, however it's a better option if you have any dynamic/API parts to your site because you can integrate all of that in a single place in your Worker script.

There's a bit of background here https://developers.cloudflare.com/pages/migrations/migrating...

TL;DR: Workers Sites is basically an elaborate Worker template (which you can modify) and allows you to deploy your sites using the Wrangler CLI — it'll take care of uploading your assets and all, but you're responsible for setting up CI, etc for a continuous deployment experience.

Cloudflare Pages, by contract, integrates directly with Github, which allows us to offer a lot more features out of the box, including running your build, preview URLs, etc.

Hope that makes sense.