I get it now.
In our case we have a large ZFS pool, therefore we could create multiple datastores backed by the ZFS to server multiple clusters. (Because each store has it's own filespace.)
pool/store1 --> Cluster Red
pool/store2 --> Cluster Blue
But you can't do pool/store1 --> Cluster Red and Blue... Unless you for sure don't have a clash of VM/CT IDs.