I think placing one's shadows in Zone IV also has to do with what one meters as shadows,, that is, the darkest areas that you wish to print with full detail, and correlating these to the actual values as you desire them to be in the final print.
I find Zone IV easier to identify in a scene, so I meter for it, but intend it to be a Zone IV.
Knowing film speed is critical, of course. If you do know it, you can of course place your actual shadows in Zone IV, and being aware that this exposure will affect your highlights, adjust your development accordingly.
A properly exposed and developed negative should look quite good on a proof that is prepared on your standard grade, printed with the minimum exposure to achieve maximum black. Not that every one is going to be just right, but I think aiming for this allows you the leeway you need to make your best prints consistently.
As someone said above, there is little you can do to save a negative that is underexposed, but you can burn in the highlights from an overdeveloped negative. While this is true to a degree, it is much easier to get an excellent print with a properly exposed negative, that is developed to place the highlights where you want them.