2.5.4 Effect on Accounts
Windows domains have an effect on the way that accounts and groups work. Some of this is by convention, and some is by design.
By convention, when a Windows-based system is added to a domain, the domain administrators group is made a member of the local administrators group.
By design, groups have different scopes when domains are involved. Groups can be defined to be globally known and therefore usable by other domains or known only within the domain in which they are defined.