I would argue that you are doing both: you are writing documentation for the people that were not there when you wrote the code, but also for the people that were, but have worked on several other things in the meanwhile, so they might have forgotten about all the details.

Trying to improve the chaos called work - one article at a time. Blogging on Medium and on my blog chaosverbesserer.de.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store