I will say it up front, I don't load for the 357Max. Having said that, I will aver that there is only two reasons that I am aware of to crimp a case. The first reason, which has already been stated, is to keep the rounds that are in the magazine from moving their bullets from recoil inertia, and second reason is to initiate consistant ignition. I think you can decide by the accuracy or lack thereof whether you need to crimp the case mouths. If it were me, I would crimp them because that is what I do with straight walled pistol/revolver ammo.