MacMost Now 900: Manually Managing Media On Your iOS Device
Instead of using sync settings to decide what music to put on your iPhone, iPad or iPod touch, you can set iTunes to let you manually drag and drop music and video into your device. This lets you have finer control over exactly which songs are on the device. You can also get media on to your device without it needing to be in your iTunes library. Another advantage is that you can transfer media from a second Mac to your device without needing to erase the existing media.