Not only is it unnecessary, it adds a variable that can introduce variation in your loads, not a good thing. Neck crimping in necessary to hold the bullet in place when the round is introduced into a tubular magazine and, in some BPCR like the 45-70 with light bullets, to hold the bullet in place while the charge ignites. The 405gr bullet appears to be started into the barrel by the primer impulse, crimping it keeps it in place until the charge ignites - a matter of microseconds, perhaps, but apparently important.
I've never neck crimped for a bolt gun.