Short Answer: Better Career Opportunities through Better Image
Just knowing your field of work is only the beginning. In order to get a competitive edge, you need to work on your image. It is not enough to be able to do your job well, that is a must, but you need to make people around you feel comfortable about you.
When you are certified by a world standard like IITTI, you are telling employers that you are aware of the importance of good manners in the work place, and that you have the necessary knowledge and training to perform with decorum.
Most importantly, when you have a certificate from IITTI, it shows that you have taken the time, energy and money to learn about good corporate etiquette. It shows that you care about people and business relationships. It shows initiative.