[Samba] Samba 4 DC - idmap config on a samba 4 member server

[BOTZ Franck (Informaticien) - DDT 67/SG/MGI/CI]

Without idmap line, it work too.

[global]

    workgroup = DDCS
    security = ADS
    realm = DDCS.LOCAL
    encrypt passwords = yes

#   idmap config *:backend = tdb
#   idmap config *:range = 70001-80000
#   idmap config DDCS:backend = ad
#   idmap config DDCS:schema_mode = rfc2307
#   idmap config DDCS:range = 500-40000

    winbind nss info = rfc2307
    winbind trusted domains only = no
    winbind use default domain = yes
    winbind enum users  = yes
    winbind enum groups = yes

What is the really role of idmap's line ?

I have of to miss something