Hi Sac,
it is used especially in product compliance scenarios to generate a bill of substance out of a bill of material in which you can go down to the substances level contained in a material/component to make sure the whole BOM is compliant with legal mandates like RoHS and other substance level compliance mandates.
Bill of Material Transfer - SAP Product and REACH Compliance - SAP Library
This transfer of BOMs can be from within SAP ERP or from a legacy PDM tool.
Regards, Ulf.