I think I remember reading somewhere that the narration was added lade in production. I'm not exactly sure why, but I guess with all the scenes they ended up cutting, they figured the narration could work as a sort of plot-glue, keeping the scenes connected.
But even so, I don't know if it's actually needed. If it adds much. I would love to see a version of the movie with the narration removed. I like the idea of the visuals itself and the incredibly expressive characters driving the story.
What do you guys think? Do you think the movie would have worked without the narration? And if not, what about the original cut?