Our subject matter can, but doesn't always, fall exactly where we might prefer it on the print. Heck at the contrast rate we want (where we get the right "snap" in the print) all the subject matter we want might not even be visible.
The grey card is a "stand in" for mid tone subject matter. When I look at a photo, one of the things that stands out for me is whether or not things look "as I would expect". If mid tone stuff (like a grey card or face or building or coyote) falls too light or too dark, in relation to what I expect from a real situation, it looks weird, wrong.
Moving the mid tones around a bit with a bit of burn or dodge can make a huge difference. Getting say the shadow point and the grey card right and then burning in the highlights may work better, or get the highlights and mid tones and burn or dodge the shadows.
Reference points give us a way to figure this out with enlarger meters or test strips.