I have a .375 Ultra round in front of me here which may help explain why I crimp. This rifle is almost always loaded, and I often add rounds to the top of the mag without changing out the rounds on the bottom. So let's do some measurements.
I resize my .375 cases with a Redding sizing die, and seat the bullet with a Forster seating die. A freshly loaded round has an OAL of 3.557", and a case length of 2.835". The shoulder of this case measures .512".
By contrast the round which had several firings take place over it, has an OAL of 3.515, case length of 2.833" and the case shoulder measures .521"
The bullet from the round at the bottom of the magazine shows evidence of impact, but was a flat tip round nose to start with. The unfired round has the forward edge of the crimping groove visible, the round from the bottom of the magazine does not. In my opinion, if there is enough recoil energy acting on that round to drive a crimped bullet into the case until stopped by the forward edge of the crimping groove and to expand the case shoulder, then I suspect that the bullet, if left uncrimped would be driven into the case until stopped by the powder column.
In addition to the potential of a bullet moving in the case neck, if we consider the fact that a properly crimped bullet produces a more uniform pull weight than does a non-crimped bullet, there would seem to be no downside to crimping if;
A) the bullet has a crimping groove
B) the bullet is not seated long enough to contact the grooves in the barrel.