Benefits

Using OpenSSO Enterprise as Service Provider

You are likely to leverage WS-Federation in a mixed environment involving Windows domains and heterogeneous web service environments. In such cases, using WS-Federation eliminates the need to complete the complicated setups involved with Desktop SSO (IWA, Kerberos, etc.). This simplifies the integration of web services in the ADFS-based environments.

Using OpenSSO Enterprise as Identity Provider

The immediate benefit is the single sign-on to SharePoint Services from non-ADFs environments. This can be extended to pure claims-based applications residing inside the Resource Partner's domain.