The source content for the Dispatch Router book is captured in large, monolithic files (generally one file per "chapter"). This makes it difficult to reuse content within those chapters, and difficult to structure the book according to user needs. It also forces the content into a linear, book-like model.
Modularization seeks to resolve these (and other) shortcomings by refactoring the monolithic content into assembly and module files. An assembly file describes how to complete a single user story. Assemblies transclude module files. A module is a single procedure (how do i ...?), concept (what is ...?), or reference (a set of detailed facts in tabular form). In short, modularization ensures that all content is based on user stories (and therefore relevant to the user) and strongly information typed (and therefore concise and on point).
By implementing modularization using assemblies and modules, highly customized deliverables (such as books, articles, or web sites) may be created, and the individual assemblies and modules can be reused and combined in whatever arbitrary structure is best suited to the deliverable.