In Spanish: a page describing the benefits of identity federations, together with the advantages of a multi-protocol hub like SIR: http://www.rediris.es/sir/beneficios.html
In Dutch: A pdf document describing SURFfederatie and the benefits from the viewpoint of IDPs, SPs, and users. Contains some use cases/best practices from connected IDPs/SPs: http://www.surfnet.nl/Documents/SNA4fedWeb.pdf