If there's something that GIMP can do that Krita can't, I never encountered it in over two years of using it for front end development and graphic design work.
Same here. I don't do much in Krita but it has been able to do everything I wanted gimp to do, but just nicer of a tool.
There are some photo-specific effects and tools present in GIMP that are missing from Krita. I remember having to switch to GIMP for some edits, but I can't recall the specific features. 95% of the time, though, Krita is all you need for photo editing.
I can't find the resynthesize function in Krita for one.