When to use "Included Projects" and "Clusters"

Hi,

Could someone please explain when to use Included Projects and Clusters in Citect?

If I had 2 projects, e.g. MachineA and MachineB and wanted to combine them into 1 project, assuming that both machines are identical but currently running independently of each other, would I:

-Include them both under a master project,

-combine the projects together and separate them using Clusters,

-use a combination of Include and Clusters?

Thanks,

Etienne