samba - Nov 2007 - slow perf without winbind nested groups = no and ldpa backend

Helo samba list,

We are using a samba (3.0.25b-1.el5_1.2) PDC ( users are in an LDAP 
backend ).
The perfs were bad  and there were errors until I set winbind nested 
groups = no  in smb.conf.

I saw this post
http://lists.samba.org/archive/samba-technical/2005-May/040946.html
saying

"What I would like to do is to make clear that people should always use
idmap_ldap when they use ldapsam." 


I have no needs for winbind and no idmap backend is set.

am I wrong ?
what is the link with "winbind nested groups" option ?



thanks in advance for your answers.


jmp