An open stance promotes a high sift shot with landing power. An open stance simply means that your body lines {feet, hips, and shoulders} are positioned more left of the target line than with a square set up. The purpose of an open set up is to promote a slight out-to-in path, which produces a high, soft flight with stopping power.
With an open stance, your body lines are positioned {angled} more left of a square set up.