The InvoiceStaffingSupplierSite property sets the user's default branch for all invoices in a billing batch. Any other value than UserStaffingSupplierSite will set the invoice branch to its corresponding Customer's branch. This option is mainly used when there are multiple staffing suppliers that need to share the same customer. This option allows the users to use the correct branch for the invoice i.e., based on which branch the invoice is being processed from, rather than always using the same customer's branch.
Admin Tools location:
Config Option > Supplier > EmployerSetting
CustomerBranch: Sets the invoice branch to the corresponding customer's branch.
UserStaffingSupplierSite: Sets the branch for all invoices in a billing batch to the user's default branch.