Smarts is a Smart Playlist Manager
Smarts will save and store the criteria of an iTunes Smart Playlist -- the "smarts" of a Smart Playlist -- as a template so you can reload it into iTunes later.
• Use Smart Playlist "Starter" Templates •
Perhaps the best use of Smarts is to maintain several "starter" Smart Playlist templates of your frequently used criteria (eg: Genre is not Holiday or Last Played is not in the last 6 months). Instead of painstakingly re-entering the same basic -- and perhaps elaborate -- criteria over and over again, just load a pre-made "starter" template as a new Smart Playlist in iTunes. Smarts can even open the Smart Playlist Edit window for you automatically after the template is loaded so you can easily provide additional criteria. (Smart Playlist criteria can only be edited in iTunes.)
• Reduce the Number of Active Smart Playlists •
iTunes performance is smoother when there are fewer active Smart Playlists to continuously maintain.