Even with the most frantic half effort of a project, its helpful to give the context of why you are doing it, why you approached the project this way, and why you ended up not going with another approach. Maybe you did try what should have been the best approach at first, and it didn't work right, so you had to do something not as good but good enough. Then in the future someone decides to try to redo what you've done using the best approach, and they hit a wall because you never wrote down that you tried that and it didn't work for x reason. Writing up what you do helps keep your own thought process organized, so it's beneficial for you even if you never read what you wrote.