Well said. I was thinking about what some instructors have said to me in the past and I want to add a couple of things.

1. There are instructors who are basically poor group fitness instructors who just wind up frustrating you with weird choreography (quick count jumps between seated, standing, and climbing positions, for example-- how can you figure out your pedal stroke, general form, or cadence?), where the best thing to do during those sets is your own thing as has already been said.

2. Then there are the spin instructors who kick your butt, incorporate a lot of anaerobic intervals and steep climbs, improving your power, recovery time, and strength, yet also being very hard on your body. You walk out feeling beaten up, but you loved it (good teacher even if more drill sergeant).

3. The final group tend to be real road riders who may do an endurance ride or may do an intervals ride, focusing on HR zones and/or cadence, but you walk out ready to go another hour, feeling energized, limber, and not injured.

Good strength building and anaerobic training is useful, but I think the classes of that type should maybe follow a ride of the 3rd type or at least be not the dominant type of spin training you do. I think those lead to tendon, joint, or muscle problems if overdone. (The first group is nearly a waste of time, but at least you get to spend some 'me' time on the bike and can hopefully turn it into a decent workout.)

[There is a 4th group who is a better group fitness instructor than #1 but not a road rider and softer you than #2. There you can enjoy the good parts and ignore the stuff too much like a generic cardio class if you're not into those things--sometimes they help break up the boredom if done well with a better teacher.]