To build code that is robust and maintainable, it matters a lot how the code is divided into components, how these components communicate, how changes propagate as they evolve, and more importantly how the programmers who develop these components communicate as these components evolve.

If your work affects other groups, might be reusable across groups, adds new components, has an impact on other groups (including QA or Ops), or otherwise isn't purely local, you must write it up using at least a couple of paragraphs, and get a design approval from the other parties involved before starting to write code — or be ready to scratch what you have when they object.

If you don't know or don't care about these issues, ask someone who does.