Stock Transfer between Storage Locations in the same Plant

Hi,

I'm trying to setup STO between Storage Locations in one plant and the settings in this IMG path are really annoying me :

SAP Customizing Implementation Guide

Materials Management

Purchasing

Purchase Order

Set up Stock Transport Order

Set Up Stock Transfer Between Storage Locations

Define Shipping Data for Stock Transfers Between Storage Locations

So for each Plant / Storage Location combination I can maintain a Shipping Point, a Vendor, and a Customer.

When I create my STO, I can see the change of the Customer depending of the Storage Location, but what is the Vendor used for in a single Plant scenario ?

More importantly, what is the use for the Shipping Point in this IMG transaction ? My Shipping point gets determine by the Customer Shipping Conditions and the Material Loading Group.