I find that "quiet leadership" keeps me more calm and more in control of myself. As we all know, these are the two keys to leadership. If you are not in control, you cant expect your dog to follow your leadership. But that doesnt mean that there aren't a few times that one needs to be "heard".
To that end, Ive always used a bit of sound when I feel that I need to. I dont rely on sound all of the time, but I do use it to get a point across. My feeling has always been that Dogs use sound to relay information to each other, so it is only natural for us to relay infomation in the same way.
For instance: If I give the "sit" command and while sitting, one of my dogs moves, I simply give a "NO" or "AH-AH" followed by a hand signal to reset the command. It works everytime.