I liken it to the differences between a telephone call and an email.
If you are trying to do something that requires to and fro and responses and reactions, an email exchange is laborious, while a call can be incredibly efficient or productive. But if you are giving directions, emailing an address and a map is way better.
To expand on that a bit, timely feedback is critical in the learning process, what I referred to above as “formative assessment.” For example, when the new student attempts to load film on a stainless reel, it is common to use some scrap film in the light to practice. Even under those conditions, not every student will be successful the first time. A teacher can observe what they are doing and provide feedback in the form of constructive criticism and guidance during the process in stages. When the film jumps the track, those of us in the know will recognize that by sound and feel and will back it off, give it a bit more of a crimp, and try again. The novice won’t have those clues and pointing them out at the time is how the skill is built.
It is possible, although not nessesarily preferable, to learn many skills online. A student can demonstrate the skill using any of the popular live video tools that have become common over the past 2 years. Or the student shoots a video, uploads it, and the instructor can provide feedback referencing the time stamps.
A friend and I were talking about this just the other day, the importance of SEEING it done rather than reading about it. The written version tends to assume that things will go well, leaving the learner stranded when the instructions don’t cover all possibilities. In our example, we were talking about how to center the main jet in an SU carburetor, not unlike the process of loading film on a stainless reel.