November 19, 2011, 8:16 AM — We've told you what you need to know about iTunes Match. But we're also happy to share with you some secrets of iTunes Match that you don't absolutely need to know, yet might enjoy knowing anyway. Trust that tucking these tidbits away will make you the star of every party--at least parties where everyone sits around and talks about the nuances of iTunes Match.
Downloaded songs are automatically removed to make extra space
When you tap to play a song on your iTunes Match-enabled iOS device, the song gets cached. That way, if you tap to play, say, "Je Suis Rick Springfield" by Jonathan Coulton on your iPhone today, the song won't need to get downloaded all over again when you tap to play it again tomorrow. Similarly, you can tap to download complete playlists or albums on your iOS device; maybe you'd do so while on Wi-Fi so that you could hear all of Coulton's latest album later during your commute home, without gobbling up your data plan.
Of course, one of the benefits of iTunes Match is that you can free up extra space on your iOS devices by not syncing your entire library. Once you start downloading lots of songs as you play them back, does that advantage vanish? In a word: No. In more words: With iTunes Match enabled, your iOS device will automatically remove some downloaded songs over time. The algorithm is smart--older and least-played tracks are removed first.
Apple hasn't clarified under precisely which circumstances songs get removed. Perhaps one day we'll see an option to control how much storage space iTunes Match can use for caching on your device, but no such option exists yet. So while you can manually remove tracks from your iOS device by swiping as if to delete them (which leaves the iCloud-stored track in place, but frees up the few megabytes the song requires), it shouldn't be necessary; your device will take care of eliminating old tracks automatically.
Some songs aren't eligible for iTunes Match, but there is a workaround
iTunes Match won't match very short songs, and it won't match songs encoded with very low bit-rates. I found about 20 tracks in my library that were encoded at laughably low rates; each was marked Not Eligible. (You can find your tracks that iTunes Match won't match by creating a Smart Playlist where iCloud Status is Ineligible and Media Kind is Music.) We haven't found any tricks to start getting iTunes Match to match songs that are shorter than five seconds--though luckily there aren't too many of those. We did, however, come across a workaround for getting the service to match poorly-encoded tunes.