Rapid Prototyping is a great way to test the water with an idea. With a Rapid Prototype of your idea you will discover a lot. Is the game idea any good? Whats missing? Does anything need removed? This is all vital information that can be assessed early on without much time or money going into a project.
At the same time, the rapid prototype will also provide the foundation for your idea. With a prototype in place you will be in the perfect position to continue the development of your game. In some cases, if the prototype is much further along, it may even be in a position to jump straight into the polishing phase. This is ideal for teams or individuals without much programming experience as it allows them to release sooner.