I find that most lessons fall into one of two categories.
Typically, I assign most of my students material to work on for the next lesson. For older students, this might be as simple as "work something up for next week, maybe some excerpts.."
For younger students it is usually much more structured.
In that following week, my initial game plan is to go over what they've prepared and then prep for the following week.
This kind of lesson I would call the "Happy Treadmill Lesson"
But in other lessons something important comes up and we need to step off the treadmill to focus in on something. With luck, this results in some sort of minor breakthrough, replacing an older bad habit with a newer good habit.
Most common detour: making discoveries in the arena of air/relaxation.
This kind of lesson I would call the "Detour Lesson."
I often find it necessary to nudge students onto that happy treadmill. I believe there is tremendous value in the simple act of learning new pieces on a regular basis.
Generally, I find that students make less progress overall when they get stuck in a rut, either pounding away at the same piece week after week or constantly having new "revelations" about their playing.
Every now and then, I have seen a "revelations" student who was a strong self-guided learner. In those cases I try to get out of the way and let them run with it. However, other students get stuck, fretting constantly about certain details of their playing, possibly avoiding the challenges of simply having to learn new material.
Hey, in the real world, you've got deadlines. Reflection and detours can be useful but there's also something to be learned in forging ahead to meet that deadline.
In the end, you need some of both.