A partir da documentação do SuSE :
SCP is based on RCP. It allows the user to copy files over a secure channel between computers. SCP is non interactive, meaning you will have to know where the file is you want to copy and you will have to make sure the destination path exists. It is a nice way to quickly transfer a single file or a directory (in recursive mode) to an other computer. If you are interested in a more interactive way of accessing, downloading and uploading your files, you probably want to use SFTP.
de man scp
:
-i identity_file
Selects the file from which the identity (private key) for public key authentication is read. This option is directly passed to ssh
Ele é usado para apontar para o arquivo que contém sua chave para autenticar sua cópia protegida