Your back is very important for posture and balance. It is the core of your body which is needed tobe strong for many exercises. This exercise is good for the mid and upper back, lats and deltoids. Back dumbbell flys requires good form to prevent injury. Heavy weight is not needed for this exercise. Back Dumbbell Rows are great for mid back and lat muscles. This can be done with heavier weight but remember to keep back straight to maintain support.