Companies choices in stone progressions, why so many??

So I mostly use a 1k, 3k, 5 or 6k finishing stone, use Jon's Awasedo for the final final step. The edges that result are great and I can't imagine needing anything more.

My question is why do companies like Naniwa make progressions like 400, 600, 800, 1000, 2000, 3000, ...

Is this only for polishing out scratches? I find it very hard to imagine that using an 800 instead of a 1000 can make a big (or any) difference for example??

(I realize that occasionally a stone in a company progression isn't as good as the next stone up or down but that isn't what I mean, I mean having stones where just the difference in grits seems too small to make a difference...)

TIA

I do not believe that the intent is for you to ever use all of the stones in progression. Offering a wide variety of grits allows the customer to choose what points on the scale he wishes to utilize. For example, my stones are 220, 400, 1200, 4000, and 8000. Someone else might prefer having a 500, 800, 2000, and 6000 on hand.

Be well,
Mikey

Mikey nailed it but...
I think a further point relating to steel/heat treatment/style of sharpening and use in the end... all tend to be factors in why a sharper might choose a particular progression.
Also, for a lot of reasons, I think the less strokes it takes you to reach your final edge or happy place the better. Another point might be: not every knife edge needs a complete progression so pending use/damage one might choose different grits.
In the end, what is not to like about choices. I think more the goal with a line of stones is you like the feel/cutting ability/style(splash and go vs soak or perhaps softer vs harder) using your wisdom or predilection to save time/effort/steel.

Do you sharpen single bevel blades? Or wood crafting tools such as chisels?

When it comes to double bevel blades like your gyuto, I'm usually in the same boat as you. I only use a medium and fine stone most of the time. But if you need to repair your knife or thin it out a rough grit is needed. Depending on the steel I might choose anywhere from a 240 to 800 grit.

When it comes to single bevel knives or chisels your rough stone are much more important. Single bevel blades generally never come with their honbatsuke, true edge. To do that yourself more time is spent on your rough stones reshaping your shinogi and flattening your bevel out. So slowly progressing up your rough stones is quite common. I will use two or three rough stones sometimes, them a few different medium and fine stones. The progression might look something like this: #240, #400, #800, #1200, #5000, #8000, #10,000, #13,000 to get my perfect edge.

Thanks for this OsakaJoe, very helpful!

No I haven't really started seriously sharpening single bevel knives, just double bevel with of course, various degrees of asymmetry but nothing beyond say 70/30

I hope to start leaning how to sharpen single bevels soon, bought a couple of vintage ones on the bay that need a tune up

You can get a really nice mirrored finish by going up the progressions from my experiences.For higher carbide steels going up the progressions may aid in the sharpening progress.For maintaining a edge most of the stones are not used at least by me.When I re-profile an edge going up all the progressions helps me maintain a proper apex and uniform scratch pattern wich may help if you are going for a polished bevel finish.