Earlier quoted context omitted.
With Fastboot, somehow an additional, non-interfering layer of computation on the server does the same loop (without having to download anything and without significantly slowing down overall client app JS initialization) Right. Typically, the way most client-side JavaScript applications (or "SPAs") work is by having a small, static HTML file that doesn't contain much content (beyond maybe a loading page). It contain…
This is actually a very good comment that helps newbies decide whether they should create/need a "universal" app or not for SPAs. To add to this, there's also the claim about code reuse.
Specifically, ember-engines provides a way to separate code into logical apps, but having them appear to be a single app. It's currently 'experimental', but in very active development.
https://github.com/dgeb/ember-engines
For us, it provides the best-of-both worlds... a single interface to the customer, without having to load up all of the code, services, etc that are used in every corner of the app.