I actually got stuck at a light with Traction Control on when I had my stock summer tires on.
After getting four snow tires it does not get me stuck anymore, but it definitely does make getting started a bit harder than it should be. TC will cut off almost all power by braking too hard. I'm also not convinced that it is defeatable. even when turned "off" it still triggers itself if you want to make the car slide (doing doughnuts in the snow was no fun
I've never had a car before the G6 that had traction control and I don't think I was missing much.