Documentation is absolutely critical. If people get promoted, move onto new roles, turn over, etc., retaining that institutional knowledge in the form of documentation is amazing. I've untangled the thought process of my predecessor enough over the course of my career... documentation is definitely a great best practice.
Just started doing the documentation, since we didn't have any that I was aware of when I started. Basically, I got tired of having to look up the same smart campaigns over and over and decided writing them down was easier, so definitely agree on that point Juli!