Most of us, including me before I became a professional singer, take a shallow breath into the top of our chest, so when we speak it can sound tight and thin.  Using correct diaphragmatic breathing, we can let a lot more air into the lungs and therefore use this air to create more resonance.  Exploring different areas of resonance will give you more projection and variety of tone in your voice, helping you communicate your message more confidently and with more authority.