Role playing has been around as a learning tool for a long time. Without defining it as such, many of us use role play as a basic tool of life. Whenever we project into the future in a kind of 'what if' scenario we are indulging in a role play of some sort, we are projecting ourselves into an imaginary situation where, though we cannot control the outcome, we can anticipate some or all of the conditions and 'rehearse' our performance in order to influence the outcome. Much of the time we are better for it.
In a learning environment role play can be a very flexible and effective tool. The tenet 'I hear and I forget, I see and I remember, I do and I understand' is very applicable here. Role play is often used as a way of making sense of the theory, of gathering together concepts into a practical experience.