Man tar why we use -f

   Device selection and switching
     -f, --file=ARCHIVE
            Use archive file or device ARCHIVE.  If this option is not given, tar will first examine the environment variable ‘TAPE'.  If it is set, its  value  will  be
            used  as  the archive name.  Otherwise, tar will assume the compiled-in default.  The default value can be inspected either using the --show-defaults option,
            or at the end of the tar --help output.

            An archive name that has a colon in it specifies a file or device on a remote machine.  The part before the colon is taken as the machine name or IP address,
            and the part after it as the file or device pathname, e.g.:

            --file=remotehost:/dev/sr0

            An optional username can be prefixed to the hostname, placing a @ sign between them.

            By default, the remote host is accessed via the rsh(1) command.  Nowadays it is common to use ssh(1) instead.  You can do so by giving the following  command
            line option:

            --rsh-command=/usr/bin/ssh

            The remote machine should have the rmt(8) command installed.  If its pathname does not match tar's default, you can inform tar about the correct pathname us‐
            ing the --rmt-command option.