Helpful features:
1) Define a background rectangle that defines the size of the exported sprites.
This way I can make sure my animations don't exceed the boundaries of the sprite I'm generating. (traditional 256x256 character image limits)
2) Display a background image to use as a reference point (e.g. animation of climbing up an object)
Right now, I have to add an object to every frame, then delete it from all frames later.