It doesn't work very well....
When you do it, the motor will look killer on the dyno, but the motor will fade badly....just ask the guys who tried it at the Reedy Race. The armature will continue to over saturate the magnets, thus causing them to discharge.
It might work in 4 cell however......there is a strange belief that zapping the magnets ahead is illegal....it's not according to the rule book.
Later EddieO