IN THE FOLLOWING CODE SNIPPET Why is the LAST line needed

%%%% faces are stored as COLUMNS in the matrix faces

facesz=faces-repmat(meanface,1,48);
[Vp, Dp]=eig(facesz'*facesz);
%%% sort them in order of decreasing eigenvalues
[V,D]=eigsort(Vp,Dp);
%%% This is the second part of the trick -- make sure you understand why
%%% this is necessary.
U=facesz*V;

A) To normalize the eigenfaces
B) Because V are the eigenvectors of Z'Z not ZZ'