How often to demagnetize mc cartridges?


Just bought a used sumiko fluxbuster and demagnetized my Lyra Etna for the first time.  Pretty nice improvements in sound!  How often should cartridges be demagnetized?
wcheng2
I was told by Dynavector that their cartridges do not need to be demagnetized. I have a ZYX that I have never demagnetized - sounds fine to me. 
Never is the correct answer. Worse than stupid concept perpetrated by people who have no idea what they are talking about. If you have a reel to reel you can demagnetize your tape heads. If you don't, throw that thing in the garbage. Your going to hurt yourself.
NEVER demagnetize anything which already has a magnet inside it for its normal operation.  Otherwise you will destroy/weaken the magnet.  This includes moving coil, moving magnet cartridges and speakers as well as your credit cards :)
Fluxbuster works fine on HOMCs.
Use it whenever you think it will improve the SQ. No set answer, every system and ears are unique.
Did you get the manual?