^ It's been so long since I've fiddled with it that I can't say for certain but I think it controls the main radio functions, changing channel, volume, preset memories, is changing what the front is doing.
There is a button to toggle headphones vs speaker but I thought that just cut out all speakers, not offering a different audio stream to the headphone socket.
I did come across some info that suggests you can disable the back panel by pushing the radio memory 3 and 5 buttons simultaneously, but I've never tried it, don't know which models of radios this applies to.