A sedentary lifestyle due to urbanisation, growing corporate culture, improved transport services is resulting in early onset chronic problems like diabetes, obesity, heart disease etc. To add to this, if we maintain a poor posture while we are sedentary (resting at one place with minimal energy expenditure) a lot many problems get compounded.
A poor posture can lead to tension headaches, acidity, worsens stress at the job, worsens depression, gives rise to additional back, neck and shoulder pains. These problems can result in overall poor performance at work, intake of pain relieving drugs, absenteeism from work, increased work load due to poor efficiency.
A very simple method of maintaining a good posture while sitting is to keep your ears, shoulders and hips in a straight line. Ergonomics is the study of how equipment and furniture can be arranged to make people work more comfortably and efficiently. If you sit right you will feel light at a desk job.
In the words of Taylor-Kevin Isaac- you should look less like a comma and more like an exclamation mark !