Always practice perfect form! Whenever you are exercising, there is a very specific way to do each and every exercise. Doing the exercise in the prescribed manner ensures 2 things:

1) That you get the most possible benefit from the activity. If you are going to take the time and expend the energy to exercise, then do it right. Using sloppy form just robs the targeted muscles of the stimulus that you are trying to deliver to them, and can ultimately waste your valuable exercise time.

2) That you don't get injured while you workout. Even seasoned exercise veterans are still subject to a muscle pull or strain, a torn ligament, a torn rotator cuff, etc. One of the best reasons for exercise is to prevent these type of injuries, but by spending a lot of time working out, some of us forget that we are still susceptible, and we allow our form or exercise speed to go off track. This results in exactly the kind of injury that we are trying to avoid!

Always practice picture-perfect form whenever you exercise, and do all exercises with a full range of motion, and at the proper speed. Don't waste your time, or get hurt while you are trying to improve your health.