I shoot 3 under, and have always used two nocks for the reasons given above. The advice usually given is to space the locator nocks so the arrow nock has a little play so it won’t be pinched at full draw. I thought this would introduce a little inaccuracy, since the arrow nock would tend to slide down to the bottom locator nock, the same as it would slide down the string if there were no bottom locator nock. For this reason I try to get the nocks as close together as I can, while still leaving a little play, more a loose fit in between the nocks than actual play.
It now occurs to me that if the arrow nock always slides down to the bottom nock, there would be no inaccuracy because of play, because the arrow nock would always be in the same place when it was shot. So I wonder if a better plan would be to make sure the fit of the arrow nock on the bowstring is loose, which I guess is generally a good thing anyway, so the arrow nock would always slide down to the bottom locator nock, and then leave a little more play between the two locator nocks?