Improper posture may put too much stress on your back and neck and lead to discomfort and damage. The key to good back posture is to keep the right amount of curve in your lower back. Too much curve (swayback) or too little curve (flat back) can result in problems. The right amount of curve is called the neutral position.
Proper posture will not guarantee a pain-free back or neck, but it may reduce your risk for back and neck pain.
WebMD Medical Reference from Healthwise