1. To learn the effects of different swingpaths. An outside to inside swingpath will cause a slice (or a shot pulled left if the clubface is closed). An inside to square swingpath is desirable for straight shots and consistency. An inside to outside swingpath will encourage a hook.
2. To recognize the type of swingpath you currently have. Knowing the type of swingpath you currently have is the key to understanding your shots. You need to recognize the type of shots that each swingpath produces to effectively analyze your swing. Watch the shape of your shots (the way the shots curve). Examine the depth and direction of your divots to further help you understand your swingpath. Identify whether you swing from the inside to outside or the outside to the inside.
3. To understand how clubface position and swingpath work together. Your swingpath dictates the starting direction of the ball. The clubface position (open, square, or closed to the target line) is the major influence on the flight of the ball. Clubface position can make the ball slice (curve to the right), go straight or hook (curve to the left.) Swingpath and clubface are closely interrelated. Try some slow motion swings to see how the clubface position can be affected by your grip and/or your swingpath.

Do.s and Don.ts
Do take some time and watch golfers practice. Stand behind them, at a safe distance, and watch their swingpath, divot direction, and note the various types of shots produced.