It's not a 'waste product' or filler - it's a very high-value feed for livestock. High protein, very palatable. And, it doesn't work as a herbicide. At least nowhere near as well as something like prodiamine or pendimethalin or dithiopyr pre-emerge, or quinclorac post-emerge. If you have clients who absolutely won't let you use herbicides, best bet is to get their grass as thick and healthy as you can, and 'train' them to expect crabgrass and other invaders.