If you’re working with others, even simple code benefits from comments explaining what it’s intended to do. Sure you can read code and get a good idea of what it seems to do, but having a quick statement from the author enables you to work faster. And if you find a mismatch between the comment and the code, it’s a smell that could mean a bug.

And for methods and functions it’s particularly helpful to have a description at the top. Many IDEs will pop this up when you’re using the method, so you can quickly confirm that it’s appropriate for your needs and get your arguments in the right order.