First of all, playing an online RPG is actually a very social experience. You have the chance to interact with people from all around the world, all types of cultures, personalities, walks of life, and so on. This is really good to keep you rounded.
A second reason to play an online RPG is because it reinforces fundamental skills needed on the job and at school or college. Such skills include teamwork, communication skills, and leadership.
Many online RPG games have teams or tribes that you join (or ones you create and invite others to join). Such teams can be set up with their own special rules, code of ethics, strategies, and teamwork outlook. This allows the players to engage in a sense of integration with others in a group setting. The abilities to function, compromise, and work together with each other for a bigger purpose are all represented through these team efforts.
Making sure you are successful in an online RPG setting requires communicating clearly and properly. It may be an informal setting, but is it necessary to think quickly to make good decisions, solve problems, and communicate clearly to assist and be assisted by others.
At times, you as an online RPG player are called to lead others as a team leader. This is actually good practice for workplace management.
And the third (last but not least!) reason to play an online RPG is because it's just plain fun! It is a great thing to do on down times, breaks from work, when the weather is not nice out, and so on. Most of these games are somewhat family friendly (there are, of course, exceptions) and appeal to a wide range of age groups.
The entertainment value of this type of gaming goes beyond just fun, too - it also allows you to escape the daily stress and issues of life for a while and release tension.