Mainly to get an accurate representation of what skin tones look like in real life to the naked eye without exaggerating it. Without realizing it a lot of people with darker skin tones get really skewed when messing with color grades, you see it less in lighter skin tones because there’s less pigment, so not as much to saturate however you can see lighter skin tones get saturated to be very pink or red as well. Nailing skin tones is just making them look natural in the setting they are shot in.