The cornerstone, the center of gravity or however you call the mask in the process of singing, becomes immediately apparent how extremely important it is for the quality, power and homogeneity of sound.
The control of support in breathing (read more at the article about breathing), while the sound finds an "open space" within the oropharyngeal cavity (read more at the article about the mouth) and the targeting of the voice towards the resonator of the mask, show us the right direction for mastering homogeneity, volume and dynamics in our vocal instrument.

The activation of the mask while singing and the support of the diaphragm in order to hold back the breath, are the two main elements that a singer is first trained in and they are the ones that "collaborate" in order to achieve homogeneity and power (i.e. the ability to project the vocal sound) at a primary stage. Almost at the same time and as the connection and cooperation of these two is improving, there comes the mouth, playing a significant role too, with the contribution of the dome in the oropharyngeal cavity and of the good articulation, in order to integrate the best possible result in the sound production of the vocal instrument.

If the sound is not guided towards the mask, then the result is a voice that's weak and blurred, has low frequencies mainly, it's lacking in "presence" (power and projection) and is incapable of maintaining a steady, resonant and homogeneous sound throughout its range.

An even worse consequence of the above is the gradual fatigue of the voice that results to hoarseness, pain and the development of callus or even polyp on the vocal cords.

It is essential that the singer understands how to project his/her sound onto the mask and learns to recognize when it is succeeded and when it's not, in order to develop a strong personal criterion, which will protect him/her from the above-mentioned risks.

I'd like to emphasize at this point, the enormous importance of complete understanding the sensation of the resonator of the mask, because it is very common for a singer to believe, that he/she has "enabled" the mask, just because he/she manages to produce a nasal sound. Unfortunately, things are not so simple.

The activated mask throughout the range of the voice ensures homogeneity of the sound, since the high notes are given strength and volume (with the assistance of suitable air pressure through the support of diaphragmatic breathing) and the low notes maintain their presence,  while the mask "uplifts" and "cleanses" frequencies, that have the tendency to weigh down.
Finally, when you join all three elements Support - Mouth - Mask, then the most open sound can be achieved, full of vibrating energy, volume and dynamics.