Growling is a strong effect to produce out of your saxophone. Use it as a strong expression, wherever you feel that would apply in a song or solo. Check out the videos I have on the saxophone music page, I’ll bet I growl in most of these songs, take notice how heavy it is and where it happens, this can give you a good idea of how I approach it at least. In rock and blues it can be used quite a bit, but I still wouldn’t over do it because when it does happen it’s more noticeable and effective.