Im not sure why you would need more than a stone and steel rod?
you can do a lot with a stone and a steel.
but when you want to re-contour angles , fix broken tips , take dings out , do a houseful of neglected kitchen knives , get ready for processing a cow it sure is handy.
once you have everything in the kitchen set to 20 degrees you seldom use the coarse again , some 320 or 800 brings an edge back quick that wasn't easily taking an edge any more because you need to knock back the shoulder
some of the new "super steels" are also hard to sharpen with just a stone , because they are so hard