Lawn is a small example, but think about how much plant byproducts are trashed : food, leaves, wood, paper, cardboard. The implication is not only in generating fuel, but could give another twist to waste management. There's already process to convert general trash to fuel. Let's recycle what can be, than convert to fuel what need to be trashed. The only things left would be non organic materials like stone and metal. Let's also be realistic in saying that every plant waste can't be composted, as the compost needs to be used somewhere and farmers already have more than enough of animal fertilizer.