Cleaning primer pockets ensures that your primers seat properly. I've seen a bloke having misfires and junking perfectly good brass that the only problem was all of the built up gunk in the pocket after multiple reloads.
Hey Sumo, neck tension has
always been "a thing" for refining accuracy.
Looking after your brass will lengthen it's lifespan as well as looking after your dies. Ejecting it willy-nilly at the range and having it bounce around on the concrete is not real good for it.
Same goes in the bush. Keep it out of the dirt, refine your technique by ejecting into your hand.
It is also a lot easier to detect any faults in clean brass.