Associating Supplier Sites to denote a relationship in the Address Book

In the Supplier Master, what are the benefits for associating Supplier Sites to each other in the Address Book? For example, you have 2 pay sites and one purchasing site that is located in region A...however, you have buyers in Region A & Region B. In the Supplier Master, there is a Purchasing site that is noted at primary for Region A.  If you show details for that site, you can also see that there is a site name for Region B (Under "Sites Using the Address") as well but you cannot link a Contact to the Supplier site referenced