We add salt to a recipe to bring out its flavor. Salt makes everything taste better. I’ve written extensively on this, but here’s a good overview: Salt in Desserts. Deciding when to start adding ingredients that toughen versus ingredients that tenderize can make a big difference in your final product. My rule is this:  the more tender you want your product to be, the more fat has to coat the flour before starting to add water-type ingredients. This is why cakes made with the creaming method are a bit less tender than those made with the two-stage method. Yolks belong on team tender while whites belong on team tough. When making American style cakes, I tend to alternate between the creaming method, which adds whole eggs after the fat and sugar are creamed and the two-stage method which adds the eggs and a portion of the liquid at the same time as the dry ingredients (plus sugar) and the softened fat. I make this decision based solely on how tender I want my cake to be. I think your question is about mixing in foamed yolks along with the fats and waiting to add foamed whites at the end. I think. Honestly, I don’t think I’d go to the trouble of foaming yolks that will be creamed in after the fat and sugar. And, as I mentioned earlier, I only fold in foamed whites at the end of mixing if I know I’m going to use a syrup on my finished cake. At the end of the day, to my knowledge, there hasn’t been a lot of “cross pollinating” of European and American mixing methods. Aside from angel food cakes and chiffon cakes, egg foams rarely play a large role in American style cakes. And most European-style cakes are fairly low in fat and so don’t bother with the creaming method. Since there is so little fat and sugar to begin with, creaming certainly wouldn’t add much lift, so they just skip that step, deferring to the eggs to provide the vast majority of Oomph to the batter.