One of the fundamentals of singing concerns muscular development.
Of course, we need to understand the importance of each exercise. Like us, they are unique as well as having many possibilities for variation!
The Three or Five Tone Exercise can be different with changes in vowel, consonant, rhythm, and dynamics. These differences cause the exercise to be varied in the ways that it can be used as it will focus on and address specific growth needs of the student.
With that said, generally, if the three or five tone exercise is used with an even rhythm up and down, step by small step with no jumps or leaps, then there is an incremental increase of muscular tension on the way up and a controlled decrease on the way down. Think of it like doing a slow bicep curl up and down.
Basically, this exercise is really good at building muscle, and this is a large part of its intrinsic value, if done with proper adjustments!