The cleanup doesn't seem to have any effect. I ran a test and I printed the files on the device root before and after the cleanup and they are the same:
['DCIM/100MZLL/IMG_0001.jpg', '.gallery/previews/DCIM/100MZLL/IMG_0001.jpg']
['DCIM/100MZLL/IMG_0001.jpg', '.gallery/previews/DCIM/100MZLL/IMG_0001.jpg']