searching for a use case

I am looking for a use case to motivate section 4 of the following spec:

http://www.oasis-open.org/committees/download.php/18058/sstc-saml-x509-authn-attrib-profile-cd-02.pdf

The use case discussed in section 2 motivates the profile in section
3, but for the life of me, I can not conjure up a realistic use case
for the profile in section 4.  Can someone provide one?

Thanks,
Tom