The reason for working on long tones from 1 to 5, at the bottom of the dynamic range, is obvious: it is the range most neglected by students and professionals alike. In order to expand our limited dynamic palette and play pp with certainty in even the most difficult and exposed concert situation, it is necessary to develop the extreme soft register. When you master this ability, you will immediately stand out from the crowd. In an audition, exhibiting this fine degree of dynamic nuance can be the deciding factor that wins you the job. Musical freedom is attained only through dynamic control.
Remember that nothing in nature, if it is alive, starts out big and gets smaller. Develop your tone from the bottom up. If this means having a small tone for a year or two in school before you build greater volume, so be it. As you grow into your tone over time, always strive to keep that soft control while increasing your dynamic range. Never surrender that.
McGill, David. Sound in motion: A performer’s guide to greater musical expression. Bloomington, IN: Indiana University Press, 2007.