Remember that tricky bit of code? The method that called a legacy library and returned an array of objects which were indexed by product IDs. Or was it product names? Even with argument and return type declarations in modern PHP, the behavior of your components can remain obscure from the standpoint of source code alone. Coding is a messy and complex business, and it’s hard to keep track of the way your systems work and what needs doing. The problem becomes worse when you add more programmers to the project. Whether you need to signpost potential danger areas or fantastic features, documentation can help you. For a large code base, documentation or its absence can make or break a project.