The utility texture is a channel packed map that can be used for various purposes. It contains a melanin (red channel), hemoglobin (green channel) estimation (both are graded) and a cavity map (blue channel).
The melanin and hemoglobin can be used for color grading; Adding more blood vessels or redness to the skin while keeping the melanin concentration, or adding a tan skin look is possible thanks to these maps. Of course, there are many other creative ways of using them!
The cavity map can be used to help the specular lobes of your shader getting these micro occlusions that are really hard to get straight from the renderer using the displacement map only.