Do I need to delegate authority?
YES. 99% of AD implementations do need to delegate authority, even if a small team is administering the environment. The exception to the rule might be when ONLY 1 administrator is in place and he is solely using the physical AD console (Keyboard and Screen physically attached to the server within the server room) and not using the Admin privileges outside this box.
The same way we have doctors specialized in different areas, we do have administrators and operators who maintain the environment. So yes, most of the time we need to delegate authority.