I disagree, you'd be surprised how many people have the mental model of various large code bases (think Linux kernel) in their minds. It's not as if you are some savant memorizing all the lines of code and it helps to differentiate between "complexity" and "a mess." :)
Linus refused to merge the kernel debugger patches for a very long time because he felt that if a bug could not be solved by thinking (and logging), then the code was too complicated.
