Either of the two preceding approaches are enough for most programmers to reap the benefits of documentation without having to spend too much time writing it. However, if you are looking for a more universal structure to your documentation, or if you and your team are not the documentation's only audience, then it might be beneficial to use an external tool such as JSDoc or Docco.

In larger organizations, it's not uncommon to have different teams working on different parts of the code. When one team needs to use a component or library that another team manages, the first team may not want to read the second team's code, or for that matter, they might not even have access to it themselves. Robust documentation can be useful in these cases by providing a way for teams to understand each other's code without having to read it directly.

Another important scenario is user customization. With the robust and powerful applications that Backbone enables, it often is...