#3 is one I've had to think on a lot recently and I think it comes down to two things: 1) When the person who wrote the code is no longer available to talk to.

#3 is one I've had to think on a lot recently and I think it comes down to two things: 1) When the person who wrote the code is no longer available to talk to. Having even a 5-10 minute chat can massively speed up my comprehension of someone else's code and save a lot of time. 2) Unused code that hasn't been deleted. I think everyone should strive to clean up their codebases. I'm not exactly blame-free here either so it's something I try to apply more and more as the codebases I work on start staying around for longer.