I think I probably answered this question above, but I’ll add a bit more here. In European-style cakes (low butter, low sugar, probably no chemical leaveners) that require whole eggs, whipping them together to make a whole egg foam is generally preferred to foaming the whites and yolks separately because of the Tenderness Factor. But, I do want to mention a Very Cool Thing about eggs here:  Whole eggs contain the perfect amount of lecithin in their yolks to whip up all creamy and beautiful kind of a like a mayonnaise. This is why just a bit of yolk in your whites will inhibit foaming while whole eggs whip up perfectly (even if it does take longer).