When do you sharpen...please don't say when dull or when it doesn't cut. I mean, your knife stll cuts but there are half a dozen chips. Or it cuts but when you strop, the leather is getting scratched by that singlebarb. Or.... when you cut, the heel cuts fine, but your tip or belly is starting to require more pressure.
This obviously all comes down to personal preference. I use a 240mm gyuto (vg10) and like to keep it like a damn razor! i hit the stones usually twice sometimes 3 a week. as soon as there is a resistance or "slide" over skin on a bell pepper for example, its time to sharpen. But I get told I have a strange obsession with sharp knives quite often..