when to replace isoclean fuse for preamp

I replaced the fuse in my ps audio preamp a few year ago with an isoclean fuse. Well the other day I was cleaning out a desk and found a paper with info. about the isoclean fuses. It said that I should replace the fuse at least once a year, I have had the isoclean fuse for at least a few years, my question is is it really necessary to change the fuse even if it is still working or are they just trying to get me to buy more fuses? thanks