Well, it depends on the sharpener. A stone, for example, needs to be washed after each use. What happens is that the lubricant mixes with the steel dust and sticks in the tiny crevasses in the stone. That serves to smooth out the coarseness and make the stone less effective. By washing it with soap, water, and a nylon brush, you dislodge all that gunk and get the stone back to where it needs to be. Other types of sharpeners, such as those that use belts, do not need to be washed, though the belts will wear down over time and will need to be replaced.