Any moving object that is taken by the flash within an acceptable distance of within 3-5 feet will most of the time, be clear... regardless whether you use the focus LED or not. Besides the xenon flash's effectiveness is also within 3-5 feet; the effectiveness of the flash can be extended to roughly 8-10 feet if the environment is completely dark. If you tried using focus LED on subjects further than approximately 5 feet at night, it would be useless sometimes.
If you use this trick and use the Twilight Portrait profile, in most cases your phone will capture very good and clear pictures within 3-5 feet radius as the flash helps provide brightness and clarity while the profile settings improves light conditions at night making it an all-round snapshot profile to use... instead of having to fumble around looking for the best profile and settings; only to have the special moment gone.