This design is used a lot in larger corporations and companies that do a lot of Quality Assurance testing for software, or software development. It has a forest and multiple trees under this. This is also very good if your company has expanded a lot through acquisitions and you need to ensure that the acquired companies can access cross-domain files.

This design approach needs to be designed from the beginning because you cannot create a new forest on top of an existing one. Windows 2003, however, makes moving domain information and migrating between two Active Directories easier, with the tools that it provides.