Spoke to my father-in-law last night. He said they do send of the blades and cylinders for spin grinding once a year and use back lapping for maintaining the edge longer - they do it every couple of weeks given they use them in a commercial application. On his home cylinder, he only back laps 2-3 times a year and hasn't done a spin grind for some years.
I have a significantly bigger yard than him (~700m2 of grass), so I imagine I will probably need to do it yearly or every second year.
Ben.
