Nested Artboards can speed up your workflow by allowing you to reuse common animations. Any changes made to the source Artboard will be reflected across any of the Nested Artboards.
Create an instance of an artboard by selecting the Nested Artboard tool and clicking in your active artboard.
With the Nested Artboard selected, find the Artboard dropdown in the Inspector and select the desired Artboard you would like to nest. Notice that once the artboard is selected an instance of it now displays on the stage.
Once you've decided on an artboard, you'll need to add the animations you want the nested artboard to use in the Inspector.
When selecting animations to add to a Nested Artboard, you'll be prompted to select whether the animation is a Simple or Remap animation.
Simple animations allow you to key start, end, speed, and mixing values on the timeline.
Remap animations allow you to speed up, slow down, or play an animation in reverse by setting keys on the timeline.