Business Units are used to configure and manage all ClickHome data as part of an organisation structure. For many clients, these are not required, and you don't need to set them up.
If you do, you can configure them any way that suits your requirements, but typically, they should represent different businesses that are managed and measured differently, especially where the majority of users only have access to the data and information about that business. You might distinguish between NSW Housing and Vic Housing, or between Contract Housing, and a Projects division. You can also create a hierarchy of business units if necessary.
Keeping in mind that users can be part of and access data in a single Business Unit, or across all Business Units, but not multiple specific business units eg Business Unit 1 and Business Unit 3, but not Business Unit 2.
Regions are for dividing up data geographically, Admin Regions are used for Preconstruction Jobs. Land and Lead region use the Lead Region list, and Construction and Maintenance use the Construction Region list. One Admin Region could have many Lead Regions, and also many Construction Regions. This represents the situation where you may have on head office location with multiple sales offices, or sales managers managing a specific region, and also a your construction teams and your suppliers manage and service different regions.