Your reminder to write
This is your reminder to write. It's not a waste of time. Do you really know something before you write it down? Are you sure your head isn't filling in all the gaps in your knowledge and providing you a false sense of understanding?
The holes become apparent when you write it out - and then you fill them.
This is especially helpful in issue debugging. When you don't see a hole in your knowledge of the landscape, you can't test what's there. Writing out what the problem is and what you've already tried both makes it easier to identify what you haven't yet tried, as well as providing a foundation for further experimentation. You can hold the knowledge you have constant while continuing to explore and gain more knowledge.
Todo lists, journaling, technical documents - they all allow us to observe and persist our own thinking. It's powerful stuff.