the functionality behind the End Customer field in the Sales Order Screen.

This functionality addresses the following: 

The Businesses want to know the end customer for an order line for a number of reasons, for example who is entitled to product support? Who is entitled to sales credits? Who is the user of sold items? 
   

If the end customer is specified when taking the order, it is possible for the system to automatically populate Install Base with the correct end customer, streamlining the integration of Order Management and Install Base. 

     If a business uses Service Contracts, you can create one Service Contract from the sales order. This feature is useful if the Sold To customer / Partner own the Service Contract for multiple end customers. (You cannot create multiple Service Contracts for multiple End Customers on a single sales order.) 

If using Partner Order Processing, it is typical for a partner to sell to a number of End Customers. You can consolidate sales to multiple end customers on a single order. 

This functionality is appropriate for those who: 

a.       Use Install Base for product support

b.      Use Service Contracts for support contracts 

c.       Want a better understanding of the sales channels used in their marketplace, i.e. who are the customers of Partners and for the End Customers 

d.      Split sales commissions between partners and End Customers