Among other things, the diamond and cbn rods will always cut more efficiently than the alumina rods that come with the sharpmaker. They can greatly speed up the sharpening process. I use them even when the edge is not “too dull”.Is the diamond for when the knife becomes "too dull"? Sorry I am really trying to understand. I appreciate your explanations!
They are just another part of the tool kit that gives the system more versatility.