[caf]

The 'binary mode' of FTP just meant not to translate line endings or potentially character set, in opposition to 'text mode'.

The advantage with HTTP wasn't efficiency, it was that resuming interrupted downloads was typically possible with FTP but not HTTP (because ranged GET took a long while to get support in both servers and clients).

[thequux]

The difference between binary and text is deeper than just line endings and character set; PDP-10's, for example, stored text 5 7-bit characters to a 36-bit word. In text mode, it would unpack that to ASCII, whereas binary mode would pack two words into 9 bytes. If you transferred in the wrong mode, you'd just get an amorphous blob of protoplasm and need to transfer again