Playlists are a core feature in Pro Tools, offering powerful ways to create, audition and select great takes. 

From the Pro Tools Reference Guide:

The ability to create playlists is a powerful feature of Pro Tools. Each track maintains a “main” play- list and any number of “alternate” edit playlists.

Edit playlists let you take a snapshot of a track’s current arrangement of clips, thereby freeing you to experiment with alternate arrangements, return- ing as necessary to previously saved playlists.

A playlist, which can consist of a single clip or many clips, can only be assigned to a track if it is not in use by another track. While you can create an almost unlimited number of edit playlists, which are shared among all tracks, each track has its own dedicated automation playlist.

Automation playlists for audio, Auxiliary Input, Master Fader, and Instrument tracks store data for volume, pan, mute, and plug-in controls. Automa- tion playlists for MIDI tracks, however, store only mute information; continuous controller events, program changes, and Sysex events are stored in MIDI clips and therefore reside within edit play- lists for both MIDI and Instrument tracks

In this video Russ shows a little known feature of playlists and how you can build song ideas fast.