Here is what happens when I connect my iPhone to the USB in my Honda Odyssey, which has a specific iPod input on the menu (as opposed to a generic USB input device). As soon as I plug it in and select iPhone on the car audio, it starts playing "About a Girl (Nirvana)". I usually want to go to youtube to find a song for the kids, but have to sit through 10 seconds of the song EVERY TIME I PLUG IN THE PHONE. The upside is that my kids have learned to like Nirvana; also, my wife's phone has some spanish language kids music as the first item in the playlist, so it could be worse. But, I'd rather not have the phone decide "you have connected to car audio, PLAY MUSIC TIME HAS ARRIVED!"

This doesn't happen with bluetooth, and rarely (???) with headphones.

On my car, when I start the car with my phone attached via Bluetooth, it random shuffles by default. However, if I start the car with my phone attached via USB cable, it plays all the songs alphabetically. The actions available on the iOS music app are also different... when attached via Bluetooth, there are "Play Next" and "Play Later" options, where as when attached via USB, these options do not appear.

As a software engineer, I think the differences stem from whether the "now playing" playlist is being managed by the phone or by the car multimedia system. As a car driver, it's extremely annoying and I'm disappointed at how poorly it behaves.