Chart of Accounts Mappings and conv level "Balance" secondary ledger

When creating secondary ledger of conv level "Balance" how can i use the COA mapping?
i would like a use case here for this secondary ledger, so after transferring the balances from primary ledger to secondary ledger, what will the business user do with these balances ?
Can i map the same COA as the primary ledger with the secondary ledger? or do i need to map different COA?