It's all relative to what expectations and parameters you set for your own workflow based upon a specific film and development regimen, and how it looks in your preferred print medium. There are no
hard rules. The Zone System is nothing more than a kind of shorthand for labeling normal dev time verus
expansion, versus contraction etc. Practitioners often place Zone II at the threshold of desired shadow detail in the original scene, and Zone VII at the upper limit of highlight containing texture; but that's based on average conditons. Films differ; and besides, how much of the toe and shoulder of the film
you recover can be altered by things like split grade printing on VC papers all kinds of other tricks. I
personally tend to visualize the film curve itself and meter placement of the values on that; but that
takes some experience. The Zone System eases you into the concept. But its all based on personal
testing to determine what you expect from it.