It is used to sign inputs for a raw transaction using specified private keys. Returns a JSON object containing the signed transaction in hex format, a boolean indicating whether the transaction has a complete set of signatures, and an array of script verification errors if any.

How is this used?

Used to sign inputs for a raw transaction before broadcasting it to the network. It allows for granular control over the signing process by specifying the exact private keys to be used for signing. Additionally it supports providing previous dependent transaction outputs, which can be useful when constructing complex transactions.