When your teeth are crooked, they are harder to clean and will wear unevenly. Your gums can get inflamed and your teeth hurt. Eventually, you will lose your teeth.
Orthodontic treatment can inhibit gum problems and prevent tooth loss.
Also, remember that chewing is the first part of digestion. If you do not chew your food properly, the rest of you digestive system will have to work harder. The harder you digestive system works, the faster it ages. Orthodontic treatment can prevent premature aging of your digestive system. It is basically the same, with a few minor differences.