Depending on the grit coarseness you can sharpen very blunt objects or refine an already sharp edge. Generally speaking, one can expect that a kitchen knife is much less heavily used than say, for example, carpenter tools or a pocket knife used to cut wood. I suppose for a kitchen knife there is no need for very coarse stones (say, below 200). Am I wrong here?
Oh absolutely, you certainly don't want to sharpen a kitchen knife on a 200 grit stone! You'll want one medium stone in case you ever need to remove a nick or something (but then you should probably take your knife to a pro at that point), and then probably like 2000-4000-6000 grits for routine polishing. (Note Japanese grit numbers are different than American oil stones).
really rough stones (used for tools) aren't suitable for knives. they can be used to remove chips, but really require a skilled hand to not damange the knife.
most knives are sharpened with japanese waterstones (most easily available & cheap). you'll do most of your sharpening with something around a 1500 grit.
if you want a real fine edge (e.g. for sushi) you can use a 4000 or even 6000 grit for polishing. but that's what it does, polish to a mirror finish - for smoothness. you won't be removing much material with a stone that fine. usually used for finishing / honing only.
Maybe this link will help you find a proper set of grits: Choosing the right grit size of Shapton stones.
For example, a 120 grit stone is recommended for grinding of the following:
- Chopping Knife (deba)
- Tuna Fish Knife (maguro-kiri)
- Knife for Cutting Frozen Foods (reito-kiri)
- Poultry Knife (gara-suki)
You can grind the rest of the kitchen knives with a stone of 220 or 320 grit.
For sharpening it seems that you can safely use something between 1000 and 2000 grit. Follow the given link to learn more.