I think it would make more sense to keep looking at the target you are shooting at until you are sure the target is no longer a threat. You will feel a bit of a prat if the target you have just put down shoots you when you are busy looking around you. That's of course you survive.
That's what the training is for. If the threat is still moving, I wouldn't be looking for another threat.
I agree that a lot of people train for it to be part of the "dance moves." For me, it's to get into the mindset that just because one threat is gone, doesn't mean there aren't other threats to worry about.
No training is perfect. No training can get you prepared for every situation. There are an infinite number of what ifs that can show why the 360 check doesn't always work. But for me it's a mindset. It's the mindset that just because the immediate threat is down, it doesn't mean there aren't other threats to consider.