My vocal coach films every single lesson & gives it to me on a disk which is incredibly helpful as it’s easy for me to go back & look at certain exercises or pieces of music covered. I found it so helpful that I film myself practicing all my instruments to catch out any bad habits that need work. With voice however, the camera doesn’t need to focus in on any fingerings or the like. It’s much harder to set up a camera angle that gets a clear shot of both hands (not to mention feet) when harping, so unless you’re moving the camera & adjusting the zoom a lot, which is fairly intrusive to the lesson flow, the usefulness of filming an entire harp lesson is somewhat limited by comparison. My harp teacher has filmed me occasionally though, just on her phone doing a particular exercise in the correct way, then emails it to me so I have a reference.
I have to admit though, every time I use tech in a lesson, despite it’s usefulness it can also get quite distracting, fiddling with settings & the like. I’ve ended up on many tangents with my teacher about using different apps, which are all great but it does cut into actual playing time.