Somehow, as a project moves forward, small assumptions and well-intentioned but poor decisions accumulate, turning hours of work into a lousy user experience. The smart teams eliminate their mistakes before they ship by using a technique called UI prototyping. Combined with usability studies, prototypes keep teams headed in the right direction. Prototyping is a means of exploring ideas before you invest in them. Aeronautic engineers use wind tunnels.
Bridge builders create stress models.
Software and Web designers create mock-ups of how users will interact with their designs. The best reason to prototype is to save time and resources. The value of the prototype is that it is a fa ade like a Hollywood set, where only the front of the building is constructed. Relative to the real product, prototypes are easy and inexpensive to create. So, for a minimal investment, you can find usability and design problems and adjust your UI before you invest heavily in the final design and technologies.