Is it worth it to json everything and always when receiving/sending a request?

Question

JSON

I mean, is there any sense, for example, to transfer POST form data while using something like this?:

fetch(domain, {
   method: "POST",
   headers: headers,
   body: JSON.stringify({
      "login": variable
   })
})

Answer 1

No, not necessarily.
Depends on the task context. I don't think there's any hidden meaning for you either. Do as you please.