The shape of the web shows dimension in low parts and shaded more higher parts adds value and strength to picture.
Light spots would be the light capturing the lighter values of the drawing, the darker values captures the shape and shadows in certain angles.
The lines on the shirt give off a perfect shape as of being wrinkled, the shadows on the face give off a light and heavy value, like light is being shined at an angle.
The value captures the texture, adds shape and vanishing points.
The more darkened the shaded areas are the more value it adds, the light areas add texture and blend into the light and heavy spaces.
The texture adds character throughout the picture, with the light blending into the darker parts, it adds more value and makes it pop.
2-Point Perspective Drawing
The cross hatching adds detail and the vanishing points adds lots of direction within the roads as the disappear into the distance.