ember.prod.js is not minified, it contains a number of performance improvements over using ember.debug.js (as much as 15% faster). To make this more obvious to folks, we have renamed the generated ember.js file to ember.debug.js.
This is absolutely not a public API, and any usage of it has no guarantee to work across versions. In most cases today, these sorts of helpers should be rewritten as components (which can easily invoke other helpers via their layout).
We have no documentation that suggest using helpers that call helpers, and as such I don’t really think that we should document that you shouldn’t do it either (we don’t document the things not to do).