If you actually get some value from re-reading and reorganising your old notes, that's great. It sounds like you don't have the problem the author is addressing

If you actually get some value from re-reading and reorganising your old notes, that's great. It sounds like you don't have the problem the author is addressing. But many people write tons of notes and save them but almost never look at them again, and subsequently worry they're wasting time writing and saving all these notes. This author is saying this worrying is misplaced, it's not a waste of time. The act of writing a note is valuable for tidying up the ideas in your head, even if you never look at them again. And that while you don't really need to save them (as you've already had the value from writing them), it can be easier and quicker to just save all your random notes, as a general policy, because trying to determine which notes have potential future utility is fairly pointless and stressful activity. Notes don't really cost anything to store. This policy doesn't work so well for physical possessions.