I'm pretty meticulous about detailed recipes, brew day schedules, and note-taking because my system is constantly evolving. I like building gadgets and trying modifications to my system and processes. Lately, I've gotten more into water chemistry as well - so there's a lot of measuring and note-taking that goes with that learning curve. Ultimately, the goal is to make the best beer I can - but I'm a systems thinker so I come up with a new idea (some good, some hair-brained) just about every time I brew.
All that said, I occasionally brew a batch without doing any of that. For example I made a small (3.5-gallon) batch of stout using BIAB on my kitchen stove this past Saturday while still in my PJs and slippers.