What is Next.js used for?

The framework's real contribution is deciding where each page is rendered. A page can be built once at deploy time, rendered on the server per request, or hydrated and handled in the browser, and the routing, data loading and bundling follow from that choice. That is what lets a marketing page arrive as finished HTML while a dashboard behaves like an app, inside the same codebase.

The trade-off is that you inherit its conventions and its release pace. File layout, caching behaviour and data fetching all change across major versions, so a Next.js codebase needs deliberate upgrade time rather than being left alone for two years. It also assumes a hosting model built around its build output, which is worth knowing if you are committed to running on infrastructure you already own.