Do yourself a favor and learn to back up using your mirrors. Your shoulders should never have to break contact with the back of your seat, even when checking your blind spots. If they do then you are turning your body too far.

 As far as the brakes go, it is a lot easier on the tires and steering components if you are moving slightly as you turn because of less resistance. I'll try to explain my reasoning as best as I can.

 On a hot summer day, if I were to turn on one spot of asphalt all the way to the left then to the right without moving with softer rubber like that found on mud tires or winter tires, and then move and look at where my tires were contacting the pavement there would be a visible black patch where some of the rubber from the tire was rubbed off. You can also hear it on the power steering pump; it has to work a lot less if your tires are moving while you turn.