This question is of interest to many manufacturers today. Why? Because more of them are making high precision, small-scale components that are critical to the function of a host of end products. A company’s livelihood may mandate that the components they use in their products are uniform, definable, and "high-precision". This is where an understanding of smoothness is helpful.
So how smooth is smooth or super-smooth? For example, is a windowpane smooth? Is a sealing surface in an automobile’s engine smooth? Is the lens in your cellphone camera smooth? And how does one define and quantify smooth? The best way is by taking a three-dimensional areal measurement and by assigning numeric parameters to the surface. Understanding the surface texture characteristics in this way helps ensure that the part is manufactured as designed and performs as intended.