I neck turn all of my serious stuff. Either use a custom die or bushing die and still use an expander mandrel. The main benifit I see with neck turning is you can keep your neck clearance consistent regardless of the batch or brand of brass. Within reason I can hit .004 clearance with any brand without having new reamer ground. Also it allows you to manage your tolerance. The less clearance there is the less you work brass and seem to get less runout. If your annealing and using a mandrel the neck tension seems to be similar between the two options but runout gets more with the more clearance you have. It's all a balance on where you feel your priorities are