but... we monitor each repetition, each series, each load day, each load week, month or year.. and nobody's monitors the rest's? is so insignificant? I don't think

I intend to make a lengthier thread about this as I have an interest in somewhat related questions.

A concept used in Mike Tuchscherer's Reactive Training Systems (RTS) is volume density; the practice of which includes setting a time cap on a particular excercise (15, 20, 25 mins, etc.). This is a means of controlling volume and the subsequent fatigue induced. When load drops are used a fatigue percentage is set to hit at which point the excercise is ceased. The problem with this is that if there were no time limit we could take, for example, 15 minute breaks between sets and accumulate huge amounts of volume across hours of training. This is not an realistic approach and there for we must have at least one constant variable (in this case time) to control volume.

It strikes me in Sheiko programs the volume is the constant instead of time. The result is the same, the amount of fatigue is controlled within limits, albeit by different means.

This is all speculation on my part trying to make sense of different methodologies. As mentioned previously I hope to make a thread specifically on this subject shortly. Not sure if my contribution is exactly what you are after but that's my take on what you are asking.