If your position in life demands that you get up on your feet and address an audience every so often, you'll recognize how important it is for your voice to live up to what you have to say.
Naturally, it needs to carry comfortably to all parts of the room. It needs to reflect the nuances of your address - the powerful statements, the asides, the jokes - so it should have a range of expression to convey light and shade. It needs to sound confident and authoritative - and you don't want it to dry up half way through.
But those qualities aren't exclusive to a few professionals. White's Technique has helped many occasional public speakers develop their abilities in this area with great success. It's also helped regular speakers improve their capabilities and become even better performers.