March 21, 2011
Smart playlists populate themselves automatically based on rules -- "Artist is Bob Dylan" gets every song in your library that lists Dylan as the artist, "Genre is Classical" gets everything that has genre setting on classical, and so on. You can create your own smart playlists by selecting New Smart Playlist from the File menu, and iTunes also creates some for you automatically to help you manage your library as you add to it. When you purchase media from the iTunes Store, it's automatically added to a Purchased smart playlist in the Store area in the left hand column of the iTunes window. If you made the purchase from an iPhone, iPad, or iPod touch, it will also appear in a smart playlist for that device. When you sync your devices with your computer, whatever you've purchased on them is automatically added to your library, of course, but those smart playlists can continue to help you remember what you've been up to.
Music you've imported into your library from your CD collection in the last two weeks will appear in the Recently Added list in the Playlists section containing all the playlists and smart playlists you create for yourself (also in the left-hand column in the iTunes window). Checking that playlist in the Sync Music tab for when you sync your devices is a convenient way to make sure you've got whatever you just added without having to think about it when you leave the house. (To change the time period, select the playlist and use Edit Smart Playlist in the File menu). As is true for all playlists, smart and otherwise, you can delete items at any time without impacting the actual contents of your library.