I think the biggest issue with the grandparent comment's approach is that it makes things extremely difficult for newcomers as was already mentioned. Turnover is inevitable in an organization and that means that eventually there will be a point where the person who wrote the initial code is no longer at the company. Touching that code is a pretty big liability if no one really understands how it works and that bogs down productivity a ton. Another reason why sometimes rewriting something is the right answer.