I'll add (3) When I'm learning a new system, especially if it's big and/or old. The idea is that if I go to the trouble to document it then the next person won

I'll add (3) When I'm learning a new system, especially if it's big and/or old. The idea is that if I go to the trouble to document it then the next person won't have to; this is seldom the case because as stated above the get out of date so fast. It's still a great way to learn and confirm your understanding though.