I'm a developer that works alone, and recently, searching for what kinds of documents I still could benefit, even though I don't require anything formal, I've read that one document that still is highly recomended to write is the project vision document.
I found it described as a short document (a page and a half or two) containing what problem has to be solved, how it will be solved and how the end user will benefit from the solution.
Reading more, it seems that this document is one extremely important input to discover the requirements and finaly the user stories.
In that case, considering that this is, as I understood, the first step when starting to build a software, what is the importance of this document, and how is it used so that it helps the development?
I still don't fully get how such a simple and short document can be that important and help that much.
How is this document important and how it is used to help the development process? In particular, what is the role of this document in the requirements gathering process?