Gattonero wrote:..... Grease or not it makes no difference.
Nope you are mistaken. If you think grease makes no difference there is a simple experiment you can do to demonstrate it; try working the sprockets (in a tightened cassette, within the backlash) against one another using a couple of chain whips. Grease the lockring before tightening, obviously.
Try it
a) dry
and then
b) with grease everywhere
In the latter case the sprockets move (within the backlash) more easily. It is the grease that gets between the sprockets and (in service) against the end faces that does the most damage.
The reason you don't grease these parts is the same reason all faces in a chainring assembly are assembled dry (apart from the threads in the chainring bolts of course). You need as much friction as possible and the easiest way to get that is with a dry assembly.
BTW there is a difference between parts that are assembled dry and then see a bit of lube vs parts that are assembled with lube from the start; the former usually have higher values of sticking friction, so are less likely to start moving around. However once they do start moving around you would find it hard to tell the difference.
cheers