The service runs in the background and launches iTunes when the phone is plugged in. It's quite handy.
That's your opinion. I always found it to be incredibly annoying, as it launches that shitty app every time you plug it in. You can't charge your Ipad without firing off ITunes. Yet another example of Apple's holier than thou concept of design: "We know better than you do, about how you want to use our products."
You can turn that behavior off on a per-device basis:
- Plug in device and load iTunes
- Find and select device in sidebar
- On the device summary screen untick "automatically sync this $iShiny when connected"
- Click 'apply'