Richard Miller's The Structure of Singing: System and Art in Vocal Technique (Wadsworth, 2001) is quite simply the best book about the process of singing on the market today.
In it he stresses the importance of knowing the details of a number of techniques of singing and compares vocal pedagogy to "a smorgasbord, from which one can sample foods both rich and simple; [but] not everything that can be ingested is equally nutritious."
Miller acknowledges that studying with many famous teachers, attending numerous of their master classes or symposiums, and reading the latest "complete" vocal method may be beneficial. But he adds that "there comes a time when the singer or teacher of singing must stop shopping around and make a choice." The right choice can only be made if "one is aware of what produces free vocal function."
Certain sounds may be exciting to the listener but harmful to the singer. Miller continues the food analogy by saying if vocal sounds "are not based on reliable functional principles, they will make the voice sick, just as a continual diet of desserts will adversely affect the constitution."
The following books by Miller are also excellent: On the Art of Singing, Training Tenor Voices, Training Soprano Voices, and Solutions for Singers.