If you have loads with a very small powder charge, especially in a .357 case, a magnum primer would be one way to insure ignition.
I cannot agree with that as a blanket statement.
I agree it's not always so. But I have had it happen to me with a light load that if the powder was in the front end of the case near the bullet I didn't always get ignition. But if I tilted the gun upward before every shot then ignition was more reliable. I retried these loads with magnum primers and found ignition more reliable regardless of orientation of the powder. I'll have to look in my book to see what they were but I think it involved 148gr WCs in a target load.