It helps fit the network to a distribution, it doesn't actually do anything other than that. This follows from basic learning theory. The actual internals of the network remain illegible. In fact it would be easy to prove that for any finite set of legible traces there are illegible ones which are equally as good when it comes to improving performance of the network.

The basic heuristic of the argument comes from biological organisms. Multicellular organisms are illegible but the overall organism still operates in its environment just fine w/o making its internal communications legible.