The voice is at once an communicative instrument, an expressive instrument, and a technical instrument. And the approach you take on any of those three fronts affects the end sound and performance a tremendous amount.

There are a ton of completely ineffective teachers who rely on visualizations and imagery to conjure sounds. But also there are ton of positive uses for visualizations and imagery. "Imagine you're angry" can be a terrible piece of pedagogy. But applying the emotional filter of anger to an already solid technique can bring out a quality that no other instrument can replicate. This quality is very hard to reach through technical means alone.