From Draw Like Da Vinci, p. 57: Getting your priorities right is the art part. Just as important as choosing what to include is selecting what to leave out. All parts must relate in harmony with the whole. The arrangement of space is equally important and should always be considered in relation to the forms.
Detail is in proportion to distance – as the figures come closer, the amount of detail drawn increases. The hair and wrinkles of the grandparents contrast with the singers' faces in the background, that are merely suggested. The child picking his nose in the middle distance is sketched in intermediate detail.