Shinny,
This is just my take, but some years back, I noticed that my cases were growing quite a bit from being turned, and when I got a new, hopefully sharper cutter, the lengthening was sharply reduced. I think that as the brass is cut, it is also squeezed between the cutter and the mandrel, which works, and probably to an extent work hardens the brass, more so with a dull cutter, and also if you go back and forth on the neck trying to make it prettier looking. While I am too lazy to turn my cases by hand, I think that the fewer turns usually involved (even though the surface finish may not be as impressive) may tend to reduce work hardening, and result in greater uniformity of seating force. For myself, I take a different approach. I cut to the shoulder feeding rather fast, intentionally leaving material behind that is cleaned up on the slow trip back to the case mouth, (and once there, never go back). This way I have the neck securely pinned between the cutter and mandrel the entire time, and can get away with a fit on the mandrel that does not produce nearly as much heat as that that some have written that they use. My necks measure very uniform.