[tomdekan]

I disagree. I think that the main benefits of personal trainers are to:

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.

[wintermutestwin]

Some people need to learn in a class with a teacher and some people are more auto-didactic.

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...