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
It's part of Isoclean's business plan.
LOL! How many hours it breaks in?
Good stuff. I thought with fuses you just remove it every year to clean the contacts if you have a dusty room or your amp/preamp can accumulate dust in there. That and the only time you replace it is when it is blown.
Change it when it blows and not a second sooner.

All the best,
Thank you Nonoise and everyone else, I will wait till it blows