While I was studying SLS I had some interesting experiences while actually singing songs.
Before I explain, let me say that mixed voice and balancing the voice is the best way to gain control over your abilities to do other coordinations. It’s your baseline. It’s the place where you return when you get out of whack. (And, by the way, you can access these great scales at Vocalize U. These scales are an octave and a half and if you can get through the scales comfortably, then you are indeed mixing!)
Speech level singing lessons are great for training sound and safe voice technique, but they leave the artist out of the equation.
My experience was when I was singing Somewhere Over The Rainbow in the key of C. The first two notes are low C to high C. You go through your first passagio at about A (ladies). My coach wanted to change my mix at high C. He wanted a headier sound on high C. I was quickly able to change it for him, but it was at that moment that I realized there must be more.
And indeed, there is.