^^^ 'zactlyIs it time for this thread again? I guess it's been a couple months. All the arguments for and against I've seen can be boiled down to this:
Pro: You tend to see whatever is behind you more frequently than you would by turning your head, and you can do so without completely losing sight of what's in front of you.
Con: It's not necessary because you have a neck. Turning your head and looking may communicate your intentions better.
Both are correct. Weigh your choices according to preference.