"Why on earth would you do that versus a straight binary transfer of the
.bin (or .iso) files themselves?"
Because the image catalog has to first be saved with *PRV release support.
And there is a note in the IBM doc that says the following:
*"FTPing Images Without Saving/Restoring and then Re-Creating the Image
These commands are run on the target system where you want to move the
images to. The image catalog object (type *IMGCLG) will need to be
re-created because it cannot be FTPed."