  We consider reciprocal metasurfaces with engineered reflection and
transmission coefficients and study the role of normal (with respect to the
metasurface plane) electric and magnetic polarizations on the possibilities to
shape the reflection and transmission responses. We demonstrate in general and
on a representative example that the presence of normal components of the
polarization vectors does not add extra degrees of freedom in engineering the
reflection and transmission characteristics of metasurfaces. Furthermore, we
discuss advantages and disadvantages of equivalent volumetric and fully planar
realizations of the same properties of functional metasurfaces.
