The major benefit for me was an emotional one, not having to worry about large stones getting stuck and then having to deal with an emergency situation, as my naturopath had cautioned (read: scared) me abaut. I don't think it produced a larger volume of stones, although I don't really know, as each flush is different.
Julia Cheng of sensiblehealth.com claims that if Gold Coin Grass is taken over a long period of time, stones can come out even without a flush...