An organizational unit is particularly useful type of Active Directory object contained in a domain. You can use organizational units to organize hundreds of thousands of objects in the directory into manageable units. You use an organizational unit to group and organize objects for administrative purposes, such as delegating administrative rights and assigning policies to a collection of objects as a single unit.
Benefits of using Organizational units are :
- Organize objects in a domain
- Delegate administrative control
- Simplify the management of commonly grouped resources.