[Samba] Join a PDC to its own domain?

[Edmundo Valle Neto]

Hello.

I have readed in several places people writing something like that when 
setting up a PDC:
now you need to join it to the domain:
net rpc join -Uadminuser%adminpass

One of them is the article "Configuration with the net utility, part 2", 
by John Terpstra
http://searchopensource.techtarget.com/tip/1,289483,sid39_gci1155693,00.html
(I dont have sure if to read searchopensource someone needs to register)

I didnt found any explanation on WHY this is needed. It is really needed?

So, reading "Samba by Example" I found something else at Chapter 5, 
Procedure 5.8, Step 21:
http://samba.org/samba/docs/man/Samba-Guide/happy.html#id2544570

...
The next step might seem a little odd at this point, but take note that 
you are about to start *winbindd*, which must be able to authenticate to 
the PDC via the localhost interface with the *smbd* process. This 
account can be easily created by joining the PDC to the domain by 
executing the following command:

|root# | net rpc join -S MASSIVE -U root%not24get

...

Have it something to do with that? Its only needed when using winbind? 
And in that case why winbind is beeing used?


Regards.

Edmundo Valle Neto