Who's talking about MP3 files and the iPod music player all of a sudden here? Your ignorance is monumental. I don't listen to music on my iDevices, but I do read books and watch movies on them, and what Tacty was writing about them is flat-out wrong.
The preferred method for handling music is iTunes Match, another cloud service that makes the same songs available across all your iOS mobile devices as well as on traditional computers. No manual transfer of songs is ever necessary.