Kerf is a term that refers to the width of the cut made by a saw. A thicker saw will make a wider cut and create more sawdust than a thinner saw which will leave more wood to be made into lumber.
The ratio of usable lumber to sawdust generated in sawmill operations has a direct relationship to kerf. Thinner kerfs yield more lumber and generate less sawdust from a given volume of wood fiber.
Every saw in an efficient sawmill is as thin as it can be to accomplish its purpose.