1. provide accountability, allowing clients to outsource some of the willpower required to exercise, and
2. motivate clients to work harder during sessions
Good form is significant, but easy to learn.
As an auto-didact, I go to one physical therapy session to learn the movements and then take those home. Tools like this (when properly advanced) would ensure that my form doesn't start slipping and helps to track improvement in RoM, etc...
It's difficult to see if the form is wrong from one angle. I need to circle around the athlete to see all the aspects. Sometimes I also ask if they are using a certain muscle, sometimes they have to "overflex" some muscle to put the emphasis on it, to make them feel it when they do a certain exercise. You can't see much of this stuff, movements are only a part of this. This is cool anyway, better then nothing for people who can't afford a personal coach