Does it even reduce latency that much (unless you have already squeezed latency out of everything else that you can)?

Presumably your backend at this point is not ultra optimized. If you send a link header and using http/2 the browser will download the js file while your backend is doing its thing. I'm doubtful that moving js to the edge would help that much in such a situation unless the client is on the literal other side of the world.

There of course comes a point where it does matter, i just think the cross over point is way later than people expect.