Manage Organization Hierarchies and Classifications

Hi All,

Could you please help us in the selection of Manage Organization Hierarchies and Classifications.
We have 3 options here 1) HCM Department Hierarchy Tree Structure 2) HCM Organization Hierarchy Tree Structure 3) None.

Please provide some useful information on below points
I) key considerations and best practices for deciding / choosing organization hierarchies type in oracle PPM
II) Is Organization hierarchies an important / significant implementation step
III) what are the objects and functions impacted by selecting the each option.
IV) what are the pros and cons of selecting dept hierarchy over org hierarchy
V) What are the significance of choosing None as an option