WSF,
It is extremely versatile,
It makes PF for IDPA/USPSA Minor with near minimum loads in everything from 115 gr to 147gr,
It makes PF with loads at the bottom end of the pressure range, thus less wear and tear on the handgun, less muzzle blast, less perceived recoil,
It meters extremely accurately,
It burns clean,
It is relatively cheap,
Loads are modest volume wise,
It is readily available,
It has a more user friendly pressure curve, (not as snappy) as Tight Group and many other faster burning pistol powders.