The only reason for a plow is to turn the cover under as has been mentioned. If it is a rocky area or roots I would certainly not use a plow. Like you said a middle buster or shovel is a lot cheaper than a plow. Also it will pull the rocks to the top so you can remove them and then go in with a rototiller and chew it up. the cover will rot a lot quicker when it is chopped. If you do plow make sure that you do not rototill as deep as you plow for at least six months to let the cover rot.