Assume that you have got slow modem/radio/cellular link that frequently disconnects and causes TCP timeouts. Not all HTTP servers support file download continuation. SMTP does not support resuming at all and heavy messages is problematic to retrieve. Moreover, each disconnect leads to the same data retransmission again, that can not be afforded sometimes.
$ nncp-file file_i_want_to_send bob: $ nncp-file another_file bob:movie.avi
will queue two files for sending to bob node. Fire and forget! Now this is daemon’s job (or offline transfer) to send this files part by part to remote system when it is available.