The main function of salt in cake recipes is to enhance
the flavor of the other ingredients. Its presence perks
up the depth and complexity of other flavors as the ingredients
meld. Salt also provides a balance to the sweetness of
cake batters—but a salty flavor should not be discernible.
Depending upon the method of combining ingredients, salt
can also have a strengthening effect if it's combined
with egg whites. If whipped egg whites to which salt has
been added are "folded in," they're better able to hold
their volume. Although salt is not considered to be an
aid in leavening, it can contribute slightly to the volume
of some recipes.
An often-cited proportion is 1/8-1/4 teaspoon of salt
per cup of flour, though other sources may cite different
amounts. There is not a specific ratio formula for home
baking. This means that the salt in a recipe may require
adjusting—for example, if a high proportion of salted
butter is included.
You can reduce the salt according to your taste, but if
you leave it out completely, you'll likely find your cakes
taste a little "flat."