How would learning SAP-FI (finance) CO (controlling) help a qualified chartered accountant?

To start using & maintaining these ERP packages these companies need people who understand SAP functionalists and have strong domain knowledge of finance as well .

I assume when you are talking about learning SAP FI/CO , you are only referring to learning implementation of the SAP ( ERP ) and not getting trained as End user of SAP . A lot of big enterprises globally use SAP ( or Oracle ) to manage and report their financials . To start using & maintaining these ERP packages these companies need people who understand SAP functionalists and have strong domain knowledge of finance as well . CAs with ERP exposure are considered good resources for such FI/CO implementation or support . These ( ERP trainings like FI/CO ) training may give you overseas opportunities , but you will loose touch with accounting and taxation intricacies for which CAs are admired by the industries . Companies like TCS , Infosys & Accenture do hire CAs with SAP certification to implement / tweak their customer's ERP system .