I believe the most significant benefit to truing an action is the effect on operational smoothness. There is an advantage in the accuracy area but a lot of how much it helps dpends on where it was before we started. Some war era mausers were not real square, but most were as slick as can be.. Sorry but like so much in life, it's not cut and dried.. I would advise the receiver ring be squared at the least. Having the bolt face trued is a good thing and as an added benefit most pitting on the boltface should be cleaned up..