Add one or more playlists to another playlist and manage the playout behavior. In some cases this can make scheduling more efficient.
Create or select a playlist.
Choose 'Playlists' at the top of the side panel.
Search for a playlist. Filter by playlist orientation.
Drag one or more playlists from the side panel:

The playlist being edited will be greyed out to prevent adding a playlist into itself.
Playlist Behavior
By default a sub-playlist will play one item, in sequence, on each loop of the main playlist. To change this behavior:
Edit a sub-playlist:

Select 'Playlist'
Preview the sub-playlist.
Select the playlist behaviour:
Play all items on each loop of the playlist.
Play a set number of items on each loop of the playlist.
Shuffle items.
If it’s a share of voice playlist, set share of voice settings.
Click 'Save':

When shuffling, the sub-playlist won't repeat an item until all items have played; making it impossible for the same item to play multiple times in a row.