A "regular" plow, also known as a breaking plow or turning plow, digs in and rolls the dirt over to one side (usually the right side). If you want to plow up a whole field, a good plow to have. A "middle buster", sometimes also known as a potato plow, digs in and turns the dirt to both sides simultaneously; great for digging up potatoes, or even occasionally other root crops, such as beets, turnips, carrots, and onions. In some cases, you can use it just to dig a shallow ditch, may or may not get deep enough to run underground water or electric lines and such. And since it turns the dirt both directions, you can make multiple passes, moving over the right distance each time, and leave "hills" or raised rows. I sometimes used mine just to tear up the ground a bit deeper before using the tiller.