Having had issues with my last lawn, and some of the various species that grew very happily amongst it, I found it was a mix, in general, the sharpening I did was to keep the blade straight more than anything, and to bring the edge down to about 0.7mm.
I never found going past about .7 or .6 had much effect, as it wore off faster, and really did not show a huge effect on the lawn, however, once the blades wore back to the thickness of the metal, or even much greater than .7, I found i was having to double take a fair bit of the lawn.
