Rather than "we don't want you to know about this method", I think the more important implication is there is no public contract on these classes/modules/methods. What this means is that we are allowed to change them according to our internal needs across releases as we see fit. The name could change, the return value might change, an entire class could go away, there's no guarantee whatsoever.

As a user, the implication for you is that if your app/gem depends on these things, it might break when you upgrade.