What is the difference between classifications of a node of an organization tree for cap ex projects

Summary:

I want to understand the difference between the classifications when adding a node to an organization tree and if there is a wrong or right choice for capital expenditure projects

Content (required):

We are using the project module for capital expenditures. When adding an OBU or department to the organization tree it get the same name listed multiple times with different classification names. OBU has Business Unit, Project Expenditure Organization, and Project Task Owning Organization. Departments have Department, Project Expenditure Organization, and Project Task Owning Organization. Does it make a difference which one I choose when adding a particular node to an organization tree?