If the Facebook code had stayed untestable and undocumented, it would never have worked at their current scale. Testing and documentation make a difference in

If the Facebook code had stayed untestable and undocumented, it would never have worked at their current scale. Testing and documentation make a difference in the long term. Unless your business model is "build a shiny tower and sell it before it crumbles", at some point, you'll have to fix the mess you made in the early days of the application.