Why should a bank finance department choose to have an ERP system general ledger instead of depending on Bank's core banking system general ledger?

This is because there are ancillary processes such as credit cards, loans etc. that are usually managed outside of the Core Banking System, that also need reporting and consolidation from a group financial reporting standpoint. For Banks that are completely dependent on a CBS for all transaction recording, an independent GL would make less sense, but we know that 90% of the banks have diverse systems built up over a period of time. In such situations, the CBS GL would only help the Fincon and Financial Reporting teams in understanding part of the picture. The holistic scenario can be mapped onto the financial reporting ERP GL, that in addition to asset and liability balances reporting, also brings with it, local staturoty reporting templates, reconciliation facility, an integration of Accounts Payable and receivables along with purchasing.

Hope this helps...

Vishnu