I think it worked and had significance in one area: the aerial stuff. I think the film works better with the aerial combat spliced throughout, with the pilot as a character that you get to know along the way. If the film was chronological, then the combat sequence would have happened right at the end, during the rescue. In fact, unless parts of it were cut, it would have made the film more back-heavy in terms of screen-time than Nolan probably would have wanted. But, cutting just the pilot stuff out of sequence would have have been really awkward. So, he made three time-lines. I agree that there isn't much of an advantage to having the "week" and "day" storylines be separate, except as a way to spread out the aerial stuff.
"-This movie has more drowning in it than any other film I've ever seen. It was usually pretty effective but still no Das Boot, which remains the all time champ."
Titanic has to be a contender, right?