iPhone Life magazine

Auto-Syncing and syncing preferences

Issue: 

A cool feature added to iTunes 9 automatically fills any remaining space on your iPhone or iPod touch with songs.

  1. Connect your iPhone or iPod touch to your computer and sync.
  2. Select your device in the left sidebar.
  3. Click on the “Music” tab. Make sure the “Selected playlists, artists and genres” radio button is clicked, and then check the box labeled “Automatically fill free space with songs.”

You can request iTunes to fill this extra space with songs from a specific playlist, highly-rated songs, and so on. Follow the previous instructions then customize your selections by checking the different items you may have in your iTunes music library. You can add genres, songs, artists, videos, etc. This function specifically lets you add more songs and videos without having to make another playlist or add one song at a time. This takes some of the busy work off your plate. 

http://www.iphonelife.com/issues/2010Winter/iTunes9TIps%2526Trick