Zone Matching is basically just a different contrast curve being used during the Image Processing Pipeline.
So, if you want a more balanced curve for both highlights and shadows, you wouldn't use the Zone Matching feature.
I've found the Hi Key handy in lighting that I'd normally get some blown highlights. But, when you use it, it's at the expense of a bit of shadow detail (which you could try to pull out in post processing). I haven't played with the Lo Key setting to form an opinon on how well it works yet.