A place for everything and everything in its place.
A writer's workload is directly correlated with the volume of content that writer must manage. Stripped down to its essence, single sourcing is a strategy that minimizes the volume of content by reducing duplication.
An obvious example is boilerplate. If you have a section about typographical conventions in every printed manual, there is no point re-writing that section every time you begin a new book. Instead, you reuse that section everywhere you need it. This is the simplest and most common form of single sourcing.
Most good writing groups will share and reuse boilerplate. If they ...