Question about Stage Function at Request Groups

Hi
The customer know the stage function is used when creating the request set. 
They want to know the usage of adding it into a request group.

I know this one as below
http://docs.oracle.com/cd/E18727_01/doc.121/e12893/T174296T174301.htm#I_orgrpgrp

Oracle E-Business Suite System Administrator's Guide - Configuration
Release 12.1
Part Number E12893-04

Section:
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Defining a Request Group
When defining a request group, you can include:

1) all the reports and concurrent programs owned by an application

2) individual reports and concurrent programs

3) request sets, which are collections of reports and concurrent programs that may be selected from