All great questions! We tend to use the A3 with the Sponsors, Process Owners and the Program Management office. They want to see the project at a glance so the one page format is perfect. It can be used the same way that the Storyboard can be used as a coaching tool. The A3 is slimmed down whereas the Storyboard allows for more detail.
The Executive Summary that is placed at the start of the Storyboard is an A3. It’s the one-page sharable summary of the project. They’re both very handy!