'How does being able to do it make a difference when you're speaking normally?' The vocal exercises drop your register immediately, particularly even a moment or two of Khargyraa will sort of... remind you that you have a lower register under your normal voice for no extra work, and sticks with you for about an hour if stressless or fifteen mins if stressed (public speaking, etc.). Also after extended use you develop the additional vocal muscles- it's like working on your core to increase your run times, by improving a range of seldom-used muscles you gain capabilities in your mains.

'Did you or any of your classmates find it did long-term harm to the high singing voice?' We weren't singing students. It was a Voice Projection for Stage class, followed by Diction and Dialects. Personally i've found that my high singing voice is more accurately pitched, but that may be due to an entirely different suite of exercises i've been pursuing simultaneously.