Overhead positions are important in developing shoulder stability, core strength, and overall lifting ability. When we say "overhead", there is need for explanation. The head itself covers an area that spans several inches so it leaves room for variations in position of the resistance. The goal is to stabilize the object. The overhead position will have the resistance over the base of support, or the mid-foot area. It will require full extension of the shoulders and elbows. In other words, we work towards lockout. Keeping this position can become harder when we start to move. Lunges and squats will add difficulty in maintaining the locked out, overhead position. We also work on locking out on other exercises such as ring dips, push-ups, handstands, and presses. Remember to use weight that you can work with reasonably and have a partner cue you. Often you will feel like you are locked out when in fact, you are not.
I am risking my good health in making examples but I think these ladies can handle some constructive critisicm. Notice the pic on the left where Corey is overhead and locked out. Ricki is mostly overhead and not quite locked out. She is close though. Karen, on the right, needs to press into full lockout, even though she is overhead.