A text based role playing game is a chat environment, where each person assumes the role of a character, and writes out their characters dialogue and action, as if they were in a story. It is at its heart a collaborative storytelling experience, a way for multiple people to write a novel, each taking a piece, and working together to develop the whole.
While it may seem a laborious task, it's actually more of a game. Each person is playing a role, akin to an actor, and yet rather than following lines, they are making everything up as they go along. It's like a session of "make believe", with a chronicle recording the actions and words used in literary form.
Aside from being a game, this can actually be a very beneficial exercise. It is a form of writing practice that is constantly refined by the social group that surrounds the person. It allows feedback for both grammar, and content. By writing in a group this way you are actually able to evolve your own literary skills.
Children who participate in such communities often receive feedback from older members with a better grasp of the written language, which helps teach them in turn how to be better writers themselves, with the hopes that one day, they can instruct others. By forming this writing exercise into a game the participants do not even know that their learning.
These games also help with socialization skills. Interacting in a fictional environment, participants are able to express themselves as they want to be. This allows them to explore methods of socialization, and interaction with other people, in a safe and non-judgmental environment.
In all, text based role playing can be beneficial for the mind and education of the players who participate. It allows people to learn better linguistic skills, while still enjoying themselves in a fairly non-judgmental manner.