Rebate Beneficiary (PA01) vs Beneficiary Address (BNAD)

For sales rebate adjustments, the documentation states to use one or the other of the subject fields but not both. Why would you use one over the other? What is difference?

For procurement rebate adjustments, the same instruction applies except for Supplier Proof of Sales which populates both. For supplier proof of sales (SPOS), the Rebate Beneficiary defaults to Specific Beneficiary and asks for a Beneficiary Address. What does this mean? If we buy promoted items from more than one supplier, does this mean we have to create a SPOS adjustment for every supplier?

For regular procurement rebates, if PA01 equals Supplier from Purchase Order, are rebates accrued for every different supplier on the purchase orders? What is purpose of PA01 Supplier from Purchase Order?