1. Improve project estimates
You'll get a clear idea of how a product will work, going through the screen flow and potentially every error condition. This will improve estimates and give you a more accurate picture of how things will work out regarding cost and time.
2. Sign off with the client
Additional client contact points means they'll feel more in the loop and know what they'll get at the end of the process. By prototyping your mobile app before starting to code you are allowing your customer to see the product working on a real device long before taking the time to code it.
3. Improve project success
Projects that capture requirements effectively are far more likely to have a successful outcome both in terms of client satisfaction and on time/on budget delivery. Prototyping is the fastest and most accurate way to achieve this.
4. Improve communication
A prototype creates a shared language that everyone can understand. You can be sure that every section of your company are on the same page and know exactly what's expected of them to complete the project.
5. Identify key user needs
Use the prototype to conduct user testing and gather feedback. This will help pinpoint the exact functionality of the product and will guarantee good usability and satisfied end users.
6. Create flexibility in design
With a prototype, different design solutions can be mocked up quickly and cheaply. Various iterations of a design can be shown to the client giving everyone more options without adding hours and hours of coding.