Any bag carried regularly, be it a purse or a briefcase, will impact your posture and your physical health. Even if its not a heavy bag the constant pressure on your body probably impacts you in ways you didn't realize.
This is especially true for women who carry heavy purses. Most tend to always carry their purse on the same side in the same position, putting an asymmetrical load on certain body parts. Take the woman in the picture above. Her right trap muscle is constantly under pressure in a concentrated spot. This could lead to over-development of the muscle, tightness and spasms. Since her right side is bearing all the weight of the bag her entire posture is thrown off leading to poor mechanics throughout her body. The size and weight of the bag might even be impacting her gait.
As with most other unhealthy lifestyle factors the best solution is to try to avoid them - like by carrying a lighter bag. If that's not an option you should minimize the impact. Try to balance the load as much as possible, by using a bag with thicker straps and alternating the side you hold it on. When possible use a backpack that distributes the weight evenly or a fanny pack that puts the load on your hips.
Don't let the weight of the bag - be it a woman's purse or a man's briefcase - throw off our posture. This is done by actively focusing on standing and walking evenly and not giving in to the weight pulling you down on one side. So pull in your abs, apply enough upward pressure at the shoulder of the carrying side to square your shoulders and pay attention to how you step as you walk, not allowing the weight to pull your feet across from each other.
Over the years we've come across a wide range of physical ailments resulting from poor bag posture. If you have an upper body ailment you haven't been able to resolve - like neck pain, chest tightness or lower back issues - experiment to see if the way you carry a bag is the culprit. The simplest test is to stop for a while and see if you feel better.