is Use of Application Modules often?

[Tony Smith]

I just noticed the topic of Application Modules:
"A new feature of Struts 1.1 is the concept of application modules. Application modules allow a single Struts application to be split into multiple modules, each with its own Struts configuration file, JSP pages, Actions, and so on."

I went over few struts books already, I don't recall any of them goes into detail about Application Modules. How often is it done in real world applicatoin development?