The basic model here lets the client verify the server, and a number of sessions secured by TLS only require this. However, some cipher suites will require the client to also send a certificate and public key for mutual authentication of both parties which as above is the client authenticated SSL handshake. This two-way authentication will, of course, add to the handshake effectively as the security increases when both the parties provide valid authentication steps to confirm the handshake, However, in some cases, the cipher suite will be needed to recommended to complete the process which in turn adds extra security to the session.