I've rarely heard this as a selling point, and it doesn't seem like a very good one to me.
Even when frontend code is clearly isolated from the backend code, it's quite easy to create a mess of it all.
Except now you're also dealing with 1) multiple separate tech stacks, 2) synchronizing state in at least two places, 3) duplication of code (validation being a common one), 4) payload size and possibly lazy-loading the front-end of your codebase, 5) and so on.
There might be /something/ to this selling point in a sufficiently large project or one where multiple client apps interact with a single backend, of course, but in and of itself I don't see the benefit of such 'forced' separation of concerns.
And by "you", you mean "you or anyone on your team"
The main selling point of these libraries is the clear separation of concerns - frontend code is clearly isolated from the backend code. Previously it was common for backends to return dynamically generated javascript and to use the DOM as a frontend data storage layer. These weren't pitfalls if you had a solid foundation but if you were inexperienced these conventions gave you a lot of rope to hang yourself with.