Yeah actually there has been an robotic arm that could be controlled via the C64.
Anyway. Which is cool about that cable is, that transferring data works in 2 directions. So you can copy files from (which is good for digitalizing them old floppys) and to the floppy, so you can play them again. I recently tested it, because I bought one and it's very nice, but sloooow. I want to digitalize all my floppies, but there occur read errors here and there, so you can't count on the digitalized versions to work, if you get this message. Which is a shame, because it means, if the floppy breaks, the game is lost.
You can even digitalize the tapes, that contain games. You just need to connect a line out from a tape player to the line in of your computer and run the cassette. If you save it as a .wav file (should be 96 khz, for best results) you can store the games forever. Of course you can easily record the Data back to a normal tape.
Which could be a bit problematic in the future is the lack of tapes or floppies in good condition to transfer back to a C64. I actually prefer the hardware and don't want to depend on an emulator.