What happens if you do not encode data in JSON?

Question

JSON

I made a small service in react/php.
But then I just thought that usually the client / server communicates using JSON.

PHP -> json_encode($data) ---- JS -> JSON.parse(response)

What happens if this is not there, what if the data is given in the form in which it is - without conversion to a JSON string?
What are the pitfalls of this?

UPD:
I have this:


If we use JSON, like this: