There are a wide variety of scenarios for Open XML development.  The following list is certainly not exhaustive, but the vast majority of Open XML use fits into one of the following categories.

Document Generation

Document generation is the most common scenario.  Insurance companies, banks, financial investment firms, direct marketing companies, and many other types of organizations need to programmatically generate hundreds, thousands, or even millions of documents on a regular basis.  In the past, many organizations have used Office automation to generate documents. 

Data and Content Extraction

Over many years, companies have archived millions of documents and would benefit from the ability to create custom tools that enable them to search through those documents. Using Open XML, companies can write custom crawlers to search the documents and extract needed information.  In some cases, companies design document templates and create internal standards to make it easier to extract the correct information from each document.

Forms and Collaboration

Through careful document design, organizations can send documents to unconnected users who then update documents with relevant information and return them.  Open XML makes it easy to extract that information from the returned documents.

Document Transformations

Publishing organizations find that they can empower users by enabling them to write content in a word processor.  Publishing systems can then transform these documents to a variety of forms, including customized HTML, PDF, XPS, text, and many other formats.

Spreadsheet Generation

Generating a nicely formatted spreadsheet for consumption by an end user is much more user friendly than generating a CSV file.  Generated spreadsheets can contain nicely formatted charts, as well as additional business logic encapsulated as formulas and pivot charts.

Presentation Generation

The most common use of PresentationML is the automatic generation of presentations.  Managers can generate presentations for summarizing performance to be presented to upper management.  Sales professionals can generate presentations tailored directly to an audience.  Sophisticated software systems enable picking and choosing slides from a library of slides, enabling assembly of presentations from a stock of professionally prepared slides.