[Samba] LDAP & Kerberos

[SvS]

Xcuse me for stupid questions... but why almost all of U are usiing
samba+ldap+kerberos, is it better than default authentication method?
And could anyone assist me in tunning this mad thing up? I don't ever
now what they (LDAP and Krb) are used for. Maybe U would be so kind to
give me some advices considering this topic or some url's where i can
find same topics disscussions. Thanks for your patience! ^)