Amano + Yoichi Stacking..

So I have read in multiple places on here about the usefulness and potency of the combination of Amano + Yoichi in endgame content but Im not seeing the real benefit. Maybe Im doing something wrong. WHat do you other dual relic Sams do? The main question I have is what exactly do you (the community) mean by the two AM's overwrite each other and whats the purpose? Should I be rotating Kaiten>Shoha>Namas? HALP.