The main task I would use the mobile app for is travel photography. For example after a hike I would like to import my photos from my camera and add a caption and a description to the IPTC section of some of the pictures so that I remember what I shot.
I don't use the mobile app yet, but this would make sense. Maybe even a GEO tagg function, like in Lightroom or Photo Mechanic to know where exactly the photos have been taken.