In another of the National Shooting Sports Foundation short training videos, Bob Whaley of Gunsite Academy discusses flash sight picture and the importance of using your sights at all times (except shooting from retention).
The flash sight picture is part of the Modern Technique promulgated by Col. Jeff Cooper. It is simply a glance at the front sight which confirms your aim as set up by your grip and stance. Whaley emphasizes that in stressful situations people revert to their training. If you train to always use your sights - even just a flash sight picture - you will use them in stressful situations. The flash sight picture is the final confirmation that you are on target before you press the trigger.
As Whaley makes clear at the beginning of the video every bullet that leaves your gun will have a 100% hit ratio. It is up to you whether it hits the intended target or something you'd rather not hit.