The BKGS leans towards qualitard builds. So you have more wiggle room in your weapon options if you need to switch things up between swishy slashy dexy weapons or the Big Boi Toys like this one.
Plus there's the bonus on all Black Knight weapons of taking the Poise in this game, which is already a joke, and turning it into a twat-swatting fight. If you're going to try outrading somebody either use Iron Flesh or a Black Knight something or other. Otherwise you're spamming perserverance or relying on Vitality.
So ultimately if you're fighting Big Bois using heavy armor, a Ultra/Great Weapon and probably the Wolf Ring+3, Then this sword kind of defeats HALF of their reason for doing that.
Off-hand a dark infused SS with BKGS and you can be pretty mean to Vitality Investors.