The roughness of a surface has a huge impact on the functionality of that surface in a particular context. Mainly, the way in which one material will interact with another material depends partly on the surface roughness of each one. If you are working with a rougher surface (so a greater degree of bumps and divots), then you can expect that material to wear out more quickly than a smoother surface would. The higher degree of friction present when using rough materials as opposed to smooth materials is also an important consideration. This can result in higher adhesion, which may or may not be the effect you are looking for. Depending on the particular part, tool, or machine you are building, you will want a different degree of surface roughness and so being able to have an accurate measure of surface roughness will be very important.