For healthy posture, the ear should form a line through mid shoulder, mid hip, mid knee to just in front of the ankle. In this position your center of gravity is balanced and stable and the minimum effort is required from muscles to keep you upright. It is the starting position for toddlers as they develop enough strength to stand and then walk. They don't have much range of deviation either way before they flop forward or backward.
As your head moves forward from this ideal alignment, it moves into forward head posture. Your center of gravity changes and your body begins to shift and adjust. If it didn't you would start to fall forward. Your spinal curvature changes and you are vulnerable to neck and back pain.
Your head weighs in excess of 10 pounds. There are many references to the fact that every inch your head is forward from the ideal adds an extra 10 pounds of stress on your neck and shoulders. Guess why neck and back pain is such an epidemic in our modern world.
Apart from the risk of injury, forward head posture decreases your height and your appearance. There are also a multitude of side effects from poor posture that increase in number as you age.
It's really a good idea to correct it. Do a Google search on forward head posture. There is no lack of suggestions, devices, and remedies. One I happen to like is the PostureJac. You will find it in the top 10 for that search word.
Forward head posture is described as carrying the head forward of the center of your shoulder. As your head moves forward, your center of gravity shifts. To compensate for this shift in the center of gravity, your upper body drifts backwards. To compensate for the upper body shift, your hips tilt forward. And this is how you end up getting bent out of shape. Your head should be in a neutral position.