I find it very useful when mentoring, especially when working remotely. I think one of the best ways to train someone to program in Rust (or any language really) is to sit side-by-side and write code while answering questions and explaining why one approach was chosen over another. Having the less experienced developer sometimes take the wheel and drive is also important.
I vigorously agree that remote mentoring and training is a prime scenario for a collaborative editor, and I've used VSCode for it (in both roles).
OT... but I would go a little further than you and say that in my experience, I prefer to have the learner drive almost all the time, and to have the mentor step in and type only when necessary.
