I am guessing that maybe it can mount the filesystem from the phone so you can play music files stored on the phone through the car audio... (?)
I bet they would sound better having the car decode them rather than having the phone play them over bluetooth.
It looks like it is designed to fit the drop in tray so I expect the L shaped connector fits into some clip so that it is easy to push the phone in/out.
Some generic cable probably doesn't fit the tray correctly.
Now that I own the cable, they should bump up my order priority, right ?