Prototyping offers designers the opportunity to bring their ideas to life, test the practicability of the current design, and to potentially investigate how a sample of users think and feel about a product.
When designers want to determine and understand exactly how users will interact with a product, the most obvious method is to test how the users interact with the product. It would be foolhardy and pointless to produce a finished product for the users to test. Instead, designers can provide simple, scaled down versions of their products, which can then be used in order to observe, record, judge, and measure user performance levels based on specific elements, or the users’ general behavior, interactions, and reactions to the overall design.
Also read Get Started With Prototyping for a more basic introduction to how prototyping is used through all the phases of Design Thinking.