It is sometimes hard to guage how well you are doing in your weight loss regimen if you do not stand up properly. Good posture will make people look at you and see your progress.
Standing very erect, with shoulders down and neck held very long, like you are being suspended from the ceiling makes an enormous difference in your appearance. This is hard to do and hard to maintain. It is good to tell the people that you see regularly to remind you when you are starting to slouch.
Also it is a good habit to stand with your navel drawn as far toward your spine as you can manage without actually holding your breath all the time. Doing this will train your abdominal muscles almost as well as a few crunches each day. Holding your internal organs in place inside your body cavity will bring you a whole new feeling and appearance. You will slouch unconsciously if your intestines etc. are hanging out and forward inside you. Again, it is difficult to maintain this unless you are always conscious of this and keep it up all the time.
Another health benefit comes from deep breathing that expands your lungs from the diaphragm instead of your upper chest. Help with this will come from elementary exercises in Yoga. Practicing Yoga, too, will help you immensely. You do not have to believe in the entire philosophy of Yoga, just do what you can with the exercises, which can keep you much more fit in general than any other discipline.
A word of warning in all this. Do not adopt a military posture. Stand tall and erect, but not exaggerated like at attention in the army. Your back can be so distorted that you will not be able to get deep breaths, and those are essential for respiratory health.
If you are a shallow or mouth breather...CUT IT OUT...every breath should expand the chest and use the diaphragm to its fullest extent. You can increase your probability of pneumonia and other congestive problems if you do not do this and deep breathing helps to oxygenate your blood, organs and muscles more fully.
It is dangerous to over-do crunches. Very often you see men who are absolutely addicted to abdominal development. They have a very odd stance, their shoulders hunched over and a compacted belly. You must do as much in developing the back muscles as you do in crunches to help draw you into a more upright stance.
Remember that the abdominals are always there. You need to tighten them up to keep your organs in their place, but it is not necessary to have them become enormous in order to show up. Instead, they will show up well if you lower your percentage of body fat. This is best done with high energy exercise rather than crunches. You should especially avoid crunches with weights.
Also, watch out for heavy loads and backpacks that are heavier than 20 pounds. Constant work on computers will also alter your posture, and if you must use one, you must be aware of the need to correct the damage every day, standing erect, back exercises, stretches etc..