If you don't decorate much (and I don't), write things where they are supposed to go (I do), and have a decent system in place (yep), your planner rarely needs a tune-up.
Still, sometimes things just need to be updated. I am not talking about revising a system, but just doing routine upkeep.
For example, my projects index was old and full of scratch-outs and needed to be replaced. I didn't change anything about my index page except to only recopy what was still relevant.
The reason that I don't change the system is that, after all, if a system is working for you, you should probably keep it. If you want to see how I use an ABC file as my Projects Index WITHOUT putting documents in ABC order, click on this link.
I also updated my budget pages. Yes, I've already spent too much this month.
I made more of the my "homework sheets" (where I track the kids' homework assignments) and more daily pages.
If you think it's time for a tune-up, just flip through your planner, looking for anything that could use some recopying or recutting, list it on a blank piece of paper, and do it. If you care for your planner like this a couple times a year, it will keep working for and taking care of you.