I'm with LC on this one. Braid is great to have as backing and will last literally forever if used just for that. I tend to use my used braid off my flipping sticks (which do need to be changed out every 6 months to a year as it is rubbing on all sorts of cover). Fluoro will last a long time if not used and abused but I would recommend changing out every year to be safe. I've been going with mostly fluoro leaders so can make a 200 yard spool last multiple seasons.
Mono does need to be changed out every 6 months at the least. I change my mono reels (I only have maybe two reels with mono) out every 2-3 trips if there is some use on them. It is cheap so why take the chance on a fish of a lifetime?
Oh, if anyone is interested, I can send my used braid for the cost of postage if anyone wants it. I have at least a few spools and will be probably making more spools soon. Delta frogging season is almost ready!!!
Todd