I bought User Stories Applied to get help with practical problems with writing good user stories and requirements in general, but it ended up changing the way I think about requirements and tracking them.
The book first fullfills one very important mission. It answers “what is a good user story” with a mnemonic rule: Independent, Negotiable, Valuable, Estimatable, Small, and Testable (INVEST). Cohn refers to William Wake as the source of this mnemonic, but expands further upon how to achieve it. For me, the most useful parts of the book was the explainations of some of the more difficult points of extreme programming’s Planning Game, such as how to split up large stories, how to estimate the effort, where to get the stories from (Cohn’s suggests using the technique User Role Modeling), and how to deal with a lack of a “real customer.” Towards the end, Cohn compares User Stories to Use Cases. For me, the discussion revealed some of the weak points of Use Cases. Based on User Stories Applied, I feel confident that the Planning Game from extreme programming addresses requirement management sufficiently for very many projects.
Reading the book made me realise the different faces of requirements and where user stories fit in. There are requirement types for which user stories may not be appropriate, but they will probably still help. More on this in later.
If you are managing requirements, especially in an agile context, this book is a must-read.