IFS effective user

Can anyone explain what the set effective user ID/group ID on an IFS
file does? From the security reference it appears to be related to
adoption since the SETUID attribute of a program/ifs is discussed in the
PA journal entry description. When is it used and what does it do? The
help text between green screen and Ops Nav seem to contradict each
other.

Green Screen:

Set effective user ID (UID) at execution time. This value
is ignored if the specified object is a directory.  The  
possible values are as follows:                          
                                                         
Yes                                                      
    The object owner is the effective user ID (UID) at   
    execution time.
No
     The user ID (UID) is not set at execution time.

In Ops Nav:

Use current thread corresponds to green screen Yes and Use object
values (owner) corresponds to green screen No.

For reference the PA entry says the following:

The type of entry. 
A Change program to adopt owner's authority. 
J Java program adopts owner's authority. 
M Modify object's SETUID, SETGID, or Restricted rename and unlink
mode indicator.

A program that adopts is set to No.

Thanks,

David Morris