What Impact does Supplier Site Primary Payment have?

Summary:

When a BU has multiple assignments to the same Supplier Address, 1 Supplier Site has Primary Payment checkbox checked; what is the expected behaviour?

Content (please ensure you mask any confidential information):

We need to interface 1 supplier site per address, per BU. Because there are currently multiple Supplier Sites per address for a BU, we are looking for a way to make the Supplier Site unique in a controlled way, without the use of DFF's. Primary Pay flag would be good because it can't be checked for multiple Supplier Sites per address, per BU. I just want to be sure this flag will not have any impact on AP.