Pivot Painter - Understanding Values corretly

@TechArt I realize this post is very old but can’t find much related information elsewhere. When fixing the vertex normals after rotating with world position offset, in this example the corrected normals are plugged into UV4 and 5. Why? Is this normally where vertex normals are stored and automatically accessed for calculation in lighting? Hoping to just plug into UV4 & 5 like this and the lighting/pixel shading pass just works.