BPC is not designed to be a general ledger system. The functionality of BPC is designed to collect, aggregate, and transform data into a reportable format. BPC is not designed to book/ create the base level entries, which should be a part of the general ledger system (i.e. SAP ECC).
BPC is also not designed to be a data warehouse. Although BPC is built on top of the SAP BW architecture, BPC is not meant to house a tremendous volume of records. BPC is to gather the necessary data for different types of consolidated reporting and only hold relevant data. BPC should not hold any irrelevant.