Anisotropic properties are defined as being "directional dependent". Rotating an object may indeed modify its illumination properties.
For such properties, UV derivatives are needed to define the U and V directions.

The Anisotropic Settings determine the U,V directions which will be used by any anisotropic properties in T2S_Illumination, i.e. anisotropic reflections or Ward Anisotropic HighLights. The parameters present in this table were adapted from Daniel Rind "BigMuh" Deriver.  

A North Vector defines wether a North Direction or a North Pole, depending on which mode is selected.

The rotation allows then to give a custom adjustment to the anisotropic direction.