One advantage of using Next.js is you can have the same React application for your entire application (marketing pages, dashboard pages, docs, etc) since it supports all rendering types (server rendering, static generation, client-side).
It also has a built-in router, instead of having to pull in an NPM package, as well as many optimizations to make your app faster (image, font, and script optimizations).
Some notes here if you're looking at migrating existing code versus starting from scratch: https://nextjs.org/docs/migrating/from-create-react-app
