Prototyping has always been an integral part of my design process. Observing users interacting with designs can often be difficult with static mocks ups or wireframes, whereas interactive prototypes provide an ideal way of gathering meaningful user feedback during testing sessions.

Screenshots of interactive prototype
Prototyping allows me and other stakeholders to test and validate the functionality and usability of a product. It also offers a better way to communicate how something behaves without the need for lengthy annotations which is particularly useful when working with off-shore teams.
I have created prototypes in InVision but I find that Axure RP to be a superior tool. It has the capacity to prototype the many use cases and advanced interactions required to achieve a fuller representation of how an end product will behave.