Reviewing and translating large documents costs time and money. New revisions of old documents can be expensive and time consuming, since reviewers usually work through both the changed and unchanged parts of the document. A modular approach eliminates this problem. A modular document consists of many separate elements (which are sometimes called "document objects") that can be created, reviewed, and translated separately.
A document object should contain just enough information so that the object is worth handling as a separate item. This obviously applies more in larger organizations with many writers and large documents.