Well.....magnets are a touchy subject....
First, we zap them all as they come from the case.....mainly because A. its possible they are not charged at all B. they are charged backwards C. they can lose charge as they sit.
Anyone who wants to dispute, is simply nuts and/or has never opened a case of motors.
Now, once the motor is built............zapping, well is kinda a crap shoot. Obviously a motor that has been massively overheated usually can use a zap or a motor near the end of its days that seems to have fallen off some. However, there is this fine line of when you DON'T want to zap. Motors have a sweetspot in magnet strength compared to the makeup of the arm. Usually the fastest motors have this......so if you zap, then the magnets begin to overpower the arm and it doesn't spin up like it used to.
A great example of this was in the 2004 Paved Nats in Portland. We had the dreaded Reedy MVP as the handout. These things had the FB9 magnets in them(same as the mods), which massively overpowered the arm and the thing generated no RPM worth a crap....and the torque simply did not make up the difference in lost HP....so, little did anyone know.....a few motors were taken up to my room.....and I used a butane torch on them to kill the magnets some.....and we finally were able to get close to that sweet spot....(EddieO brood Edition Butane Torches will be on the site shortly)....
Later EddieO