Whole eggs versus folding in egg whites
I think, as mentioned above, it really depends on how the rest of the recipe goes. If the only source of air youre getting in the cake is from whipping the egg whites then foregoing that may result in very dense cake. However, if there is a step for example that asks you to whisk butter and sugar together until light and fluffy then I think it should be fine to skip it but either way skipping would result in a denser cake.