Call me Mr Task Specific
For some knives and tasks, I'll go all the way up to 640,000 grit - and appreciate the performance difference. But not always. As another extreme, I have been sharpening knives for a local restaurant. He routinely TRASHES edges on his knives - chips and tips. Scrapes edges on cast iron pans, cuts on stainless counter tops and other horrors. So I tried an experiment, resharpening his knives (cheap ones) with a 150 grit belt edge initial AND final finish and reduced my prices. Result? He couldn't tell any difference for the work he does. Less work for me, less cost for him. Happy Happy. Task specific. If a customer can't tell the difference he shouldn't pay for an overly refined edge. For my personal use, I require a much more refined edge, but still stay within the limits of the knife to hold that edge.
Another aspect to all of this is natural stone edges. Now we get into an area where the edge type can no longer just be characterized by a simple grit rating... This in no way negates BDL's comments regarding synthetic stones but simply extends it further when dealing with natural stone edges.