The syntax of this common phrase, with the ellipses supplied, is, "Cui
homini fuerit bono negotio?" To what person will it be an advantage?
Literally, or more freely rendered, Who will be the gainer by it? It was
(see _Ascon. in Cicer. pro Milone_, c. xii.) the usual query of Lucius
Cassius, the Roman judge, implying that the person benefiting by any crime
was implicated therein. (Consult Facciolati's _Dict. in voce_ BONUM.)