Using the same controller to handle a singular and a plural route

I'm working on a rails app and using singular routes. However the controller name for the singular resource is plural. Eg map.resource activity_report expectes the activity_reports_controller. The explanation given in the rails 3 guide is: "... you might want to use the same controller for a singular route and a plural route..." That is a reasonable explanation, but what is the use case for using the same controller to handle a singular route and a plural route?