It would have provided some context, earlier in II, when Pentangeli says to Michael, "Your father did business with Hyman Roth, your fatherrespected Hyman Roth, but your father never trusted Hyman Roth..." Other than that, it's not a serious omission.

You may have noticed that, in the deleted scene, Vito looks to be about 28 - 30 years old, Roth looks to be about 17 -18. But, in Cuba, Roth's birthday cake icing says "Happy 67th Birthday." That would give him a birth year of 1891, making him only about a year younger than Vito.