If you work on client projects in a small team then a functional spec can help you keeping everything conceptual in one place and have a basis for discussion. I

If you work on client projects in a small team then a functional spec can help you keeping everything conceptual in one place and have a basis for discussion. It doesn’t have to be the most elaborate thing. A smaller project gets a few pages with some pictures, a more involved one has more explanation and database diagrams, a few stories and such. You do this work anyway, so why not write it down in a structured way? Pragmatic and simple but clear and neat. You’ll find that people do not tend to read every detail, but you can refer to the details when needed, which is very useful.