It enables the coder to engage in some late binding without engaging in a lot of casts or more elaborate metaprogramming: the enum index used for assignment is itself an assignable value and therefore can be passed around and manipulated if the algorithm needs it. It's a very intentional tradeoff of structure and long-term clarity for a faster turnaround to make design changes.

I haven't even checked to see if the final program uses it. It's the kind of thing, though, that you might go in thinking, "maybe I will need that", and it doesn't add too much overhead to your prototype.