Will renaming a function or two fix my bad behaviour?
The answer to "Should I use Math.random or X" is neither! I should be using a cryptography library like SJCL or tweetnacl-js:
Also, installed browser extensions are download-once and may need cryptographic functionality.
In some cases its impossibly/impractical to create a direct connection between 2 computers: you must use some kind of relay. If you don't want the relay to comprehend the data then you can use client side crypto on the payload. TLS still matters because it prevents 3rd parties from peeking at the communication.
Imagine a secure chat app where you want to guarantee that only you and your friend can read the communications, but want to be able to send offline messages to each other that get delivered upon connection.
One valid use, I think, could be around ensuring you don't pollute your backend with user data to avoid liability.
For example, if you wanted to use a distributed database in your backend and needed guarantees that when you delete data it is deleted everywhere at once, you could use JS crypto to do client-side encryption of the data and only have to delete the key to render the distributed data inert.
I heard about this through an article that was on HN a few weeks back (https://blog.balboa.io/yet-another.html)