When displaying bitmap fill styles, CC3 can pick from four different resolution tiles to increase display speed. These settings let CC3 know the resolution of those images. These are all preset for existing images and templates, so you are unlikely to want to change them unless you are importing fill styles.
To calculate these values, take the real world width of the highest resolution tile, and divide it by the number of pixels across. This gives you the Very High resolution values. The other values are usually 40%, 10% and 2% of the Very High value, respectively. For example, if you had a stone tile designed to be 5 ft across, and it was 1000 pixels across, the Very High value would be 200 pixels/unit and the other values would be 80, 20 and 4 respectively.