How stiffness of the egg white foam described in recipes which use egg to incorporate air for leavening?

What does the recipe say? What kind of cake are you making? Generally, you want them stiff enough to hold a peak that curls over but holds its shape when you remove the beater - a firm "soft peak". It's easy to over-beat egg whites, so when I lived at sea level, I erred on the side of slightly under-beaten egg whites for cakes. (At the higher altitude where I live now, we beat egg whites so the peaks are even softer.) ;o)