A workflow I frequently encounter is this: I need to take a JPG or PNG image, annotate it with some line art, and save it back as an image.
Photoshop is obviously ideal for this, all things being equal, since PS relates to the object as an image.
However, what I want to annotate is very Illustrator-y. I want to use Illustrator in all the ways I'm already familiar with, such as spline curves, assets already in Illustrator, etc. But then, I want to save it back out as a JPG or PNG (PNG is fine), with all the art rasterized at native image resolution. So if I come in with a 3000x4000 PNG@ 300DPI, I want it to save as a 3000x4000 PNG @ 300 DPI.
So, I want to either open or place an image in Illustrator, add my Illustrator bits and then save or export an image with the same parameters as the placed image, but with the Illustrator art rasterized onto it.