I happened to notice this feature by chance today, very cool. I notice that if you don’t select a region and instead just describe the edit, it seems to generate a different but mostly similar image with the edits, as opposed to the exact same image with only certain parts changed. It basically uses the same prompt as before but might change a small part of it.
So if it’s a very specific part of the image that needs to be changed, using the brush to select a region is better.