The Sheen channel simulates the way light interacts with lots of small threads which absorb and scatter colors.
Sheen is an RGB texture that controls the color and intensity of the sheen effect.
Tint is a solid color mixed with the sheen color.
Roughness is a grayscale texture that controls the roughness of the sheen effect.
It is useful for rendering fabrics, especially materials such as velvet, which can show strong "rim lighting" because of the way the threads scatter light compared to the angle you are looking at.