Good Day
Good Question. The Following articles will explain better
http://www.codeproject.com/KB/WCF/WCF.aspx
http://msdn.microsoft.com/en-us/library/ms731925.aspx
http://msdn.microsoft.com/en-us/library/ms731134.aspx
http://www.devx.com/dotnet/Article/38407
http://www.leastprivilege.com/CertificateBasedAuthenticationAndWCFMessageSecurity.aspx
Thank you for posting at Dotnetfunda
Vuyiswa Maseko