I initially came to the same conclusion. Though I lifted in accord with decent training principles regarding reps and sets, I didn't track for years. As I entered middle age, I started keeping a training log (just one big org file in emacs), mostly out of curiousity. As I entered my 50s, I experienced what Haruki Murakami references in "What I Talk About When I Talk About Running" --- Fat is easy to gain and hard to lose. Muscle is hard to gain and easy to lose. Now I track a couple of critical metrics and it's working great. I weigh first thing every day, track all kcals (even if I overeat), plan and track workouts. I write my own plans pulled from principles in these books (don't work for the company, just a satisfied customer) https://muscleandstrengthpyramids.com/ I don't use the vast majority of the info in those books as I'm just a hobbyist who wants to be healthy and strong. The biggest shift came from learning I was doing waaay too much training volume at the gym while trying to lose fat too quickly; a fine recipe for injury. Now, when I'm in a fat loss phase, I try to lose it as slowly as possible while still making progress. Strength training and fat loss is a very long very slow marathon, not a sprint. Perhaps paradoxically, the awareness that's come from tracking has helped me relax. No need to major in the minors; pretty good is pretty good. The tools I use are a scale, loseit, and org-mode.

The goal in bodybuilding during a gaining phase is to be in a very slight calories surplus (200-300 calories above maintenance, at most) to maximize the amount of time you're building muscle before you need to cut again (bring calories back to a deficit to shed body fat).

Tracking scale weight is difficult because shifts in water weight and hydration can swing the scale 5+ pounds in either direction without any change in body fat. So I pair scale weight with a 7-point skin caliper measurements taken on a weekly basis, along with waist circumference, in order to infer whether body fat is trending up or down. And also take weekly progress photos of 6 angles/poses with consistent lighting, which I share with a coach.

And then you pair that with weighing and logging everything you eat, and you can make small adjustments to your meal plan on a monthly basis to try to stay in that 200-300 calorie per day surplus for as long as possible. (Although most bodybuilding coaches adjust diet based purely on how your physique is changing in weekly check-in photos without the need for measurements, but I like extra data)

> down to how many reps I did of which exercise, with how much weight)

I also do this. Track every exercise, every weight, number of reps. It's necessary for knowing whether you're progressively overloading over long periods of time. Progressive overload becomes harder to measure once you're past newbie gains because you can't increase weight every week, so some weeks the goal is just to squeeze out an extra couple of reps. Which adds up over time

This is obviously excessive for 99% of people. But I enjoy doing it as a hobby. I would absolutely not recommend this level of tracking for health reasons (not necessary) - I find enjoyment in the process.

I track the reps weights of every exercise (in my own app). But the historical values are only useful up to last couple of weeks just to now if the general trends go up and what is stalled. Unless your goals are the numbers themselves and not health, I don’t think there is a reason to track everything. But it is fun.