I did that once: had a Unicode related bug somewhere in a code that fit nicely 2 A4 pages so I printed them and debug when have lunch with a friend. I was able to think a quick solution that involved few changes, probably not what I would have been go for if using a computer. One of my most debugging experience so far. Also I fixed another bug (or more likely something not in the requirements at the time) and still use that portion of code today.