This was already possible with DALL-E using the inpainting feature going from defined image to transparent edge; this just automates what was a manual process before. Do wish the inpainting tool had more options, for example to fade a transparency in, since my understanding is it makes a difference; not to mention magic wand selection/deselection tool.

In case it is not obvious, every time a user generates an additional section of an image using the outpainting feature, it costs a credit.