ipod AV cable有咩用?

it is just a cable which allow you to play music / video / photo on your tv / audio products. it is not a cable for you to transfer any data.

below is the introduction from the Apple Store

*** Quoted ***
The iPod AV Cable provides composite video and audio output for viewing photo slideshows with music on a TV. Compatible with iPod with color display. This cable is made specifically for iPod with color display (other AV cables are not compatible with iPod with color display)