GSSAPI user authentication brings the following benefits:
The user logs on to a workstation and can then automatically access all SecSh servers in the same domain and in trusted domains.
Use of Windows domain accounts.
Interoperating Kerberos for Unix. The legacy (pre-4.2) Kerberos authentication method on Unix is proprietary to SSH Communications Security. Kerberos through GSSAPI interoperates with other vendors.
Unix machines can interoperate with Windows Active Directory.
In order to gain these benefits, both the client and the server must naturally be in the same Kerberos security domain.