The main benefit is that it's very easy to have type safety and consistency between your client and your server. NextJS and the like make it feel almost like you're just calling a native JS function in your client, but it's actually doing lots of magic to make that work. The end result is your client is never out of date with your backend API, everything is type safe, you get full type hinting, and of course all of that helps LLMs write better code for you as well.