I was going to say the same that Nathan. He summarized pretty well.
I completely agree that sound & music play enormously in the immersion of your world; however games tend to change during production; sometimes the end result is far different from the original idea, and the mood & atmosphere of the music no longer matches the game's anymore.

May be a few pieces to use as "placeholder music" is a good idea like Nathan said, to see how it would fit/work; but that's all; otherwise you'll waste your efforts tremendously.