Peter, I had my 50/1.8G and 20/1.8G calibrated at Nikon service and since then I've never been in need of the in-camera AF fine tune of my D750.
At Nikon service, the rep said that the neutral position of an SWM motor will be off after using the lens for a certain period of time which will cause the focus error, and that you need it re-calibrated periodically.
The neutral position may be off even the lens is brand new. My 50/1.8G was such a sample.