Want to know the difference between performing a standing exercise versus the seated version of the same lift?  Using the example of a seated dumbbell press compared to the standing version, you’ll notice the bench supports your back and keeps your torso in place.  This will allow you to eliminate swaying action and avoid cheating; simply tell yourself that you must keep your upper back in contact with the bench and not sway forward from it.  Furthermore, because you’re keeping your torso in an upright position, you’re using more of your shoulders and less of your upper pecs.  The standing version, on the other hand, will provide the benefit of allowing you to use a greater weight – however, it’s not your shoulders doing all the work.  No matter how much you focus on isolating your shoulders, if the weight is too heavy, you’ll subconsciously employ the rest of your body.  In this case, you would accidentally be replicating the root of the “push-press” movement – a very athletic and effective exercise but one in which the shoulders are not, in fact, isolated.