Leverage your shots better too. But I gotta say, I see a lot of fighters from the caucus mountain area toilet of a place that seemingly have the opposite but MASSIVE PAYLOAD power. Beterbiev, Gassiev to name two.
Depends on the fighter. Emile Griffith had huge shoulders. I read somewhere that how a fighters clavicle are shaped might actually affect their power moreso than shoulders.
Benefits you in going up in weight. The taller and broader your shoulders the easier it is to move up in weight.