By far the biggest costs for driving instructors (ADIs*) are their car and fuel. So, it should come as no surprise that many ADIs spend a lot of time just parked by the side of the road talking (or 'briefing' as they would put it). Analysing faults, and talking through what to do, how and when to do it etc. is absolutely a part of learning to drive. However, I believe the balance should be firmly on the 'doing' side and much less on talking.
Saving money on fuel is only half the story. Many ADIs lease cars, so they can have a nice shiny new car every two or three years. If they exceed a certain yearly mileage (often 20,000 or less) they are charged an 'excess mileage fee' which can be anywhere between about 4p and 9p per mile. This is even more reason to ration your driving and increase the talk time, saving them money, and, robbing you of valuable time on the road. I don't throw money away on leasing a car, so with Fit2drive the emphasis is always on DRIVING.
Learning to drive should be challenging, not a chore. People don't learn if they're stressed, bored or daydreaming.
Enjoy learning to drive. Don't settle for dull...you know what to do.
* Approved Driving Intructor, in case you were wondering.