I am browsing images in Emacs, using Dired maybe. I happen to
stumble upon an image. While in image-mode I decide I want to edit
the image for whatever reason. Voila, your use case! :)
Then I delete the buffer, returning to my browser, and start editing
the image from there.
Starting the editor from the image buffer would be quite inconvenient
since then I would get an inconsistency between displayed buffer and
file on disk, requiring me to fiddle with revert-buffer and similar
stuff.
It would be also quite unusual if I called an image _editor_ that I
would require to display the image _afterwards_ again with Emacs.
Most image editors should be better at displaying an image than Emacs.
So killing the buffer would be a natural thing to do, anyway.
Postponing that until after the image edit is just asking for trouble.