What does code/template separation actually achieve? Ignoring JSX for a moment, why are templates a good thing? Are you actually simplifying something by using {{#each}} instead of .map()? Is {{#if}} really better than if()? Seems to me like templates don't actually decouple code.

In a large application, it starts to become a pain to deal with. It doesn't obviate the need to be careful over mixing responsibilities. In general, React components should just be things that render out to the DOM. If the HTML code is in JS, it doesn't matter as much as the more important thing of separating out your application layers.