Quickly Check or Uncheck All Songs in an iTunes Playlist
You can immediately check or uncheck all songs in an iTunes playlist by holding down the Command key and then clicking on the checkbox next to any song. There is no undo, and it’s universal for everything in the selected playlist, so if you have a carefully curated playlist be careful when you’re using this one.
This nice trick comes from The Graphic Mac as does the animated gif above showing the trick in action.
Why not check out some more iTunes tips?