Of all the teams that make up a software development project, developers are the most resistant to documentation. We hate reading, trusting or most of all writing it. Hear the call of ‘self documenting code’. A laudable target – by developers for developers, but a tester shouldn’t need to read code to understand what it does.
D3 helps developers. Story cards tend are very terse. Verbal clarification is subject to misunderstanding, lacks long-term context and leads to key-man syndrome for the architects and team leads. D3 helps spread the documentation pain. By the time a developer codes a section or page it will have complete documentation. Clarifications are added to the existing documentation. This will lead to discovery of more activation points. It is both judgement and organisational policy that decides whether the developer gathers any missing information and updates the document or whether they can pass the document back up the line.
Developers are rarely proficient at writing documentation. With D3 they only need to document discoveries at the developer level – and as with a wiki the documentation need only communicate – not be an opus. It is the job of the project technical writers to support the document.