Balance of an address is always based on confirmed transactions however there are some cases where you could need to know what is the balance of the unconfirmed transactions (potentially incoming/outgoing), that's why and based on a feedback from our clients we have added balance of unconfirmed transactions in Get Address Details endpoint: https://docs.cryptoapis.io/rest-apis/blockchain-as-a-service-apis/btc/index#btc-address-info-endpoint 


In case the transaction is outgoing this balance will be negative.
This balance is only for unconfirmed and it has nothing with the "balance" we have in general where we calculate it based on ONLY confirmed transactions.