Sizer supports multiple clusters. Each workload can be assigned to any cluster. Then in the recommendation you can view results for All Clusters or separately on a cluster by cluster basis
Here is recommendation for All Clusters, All the hardware and all the workloads are combined in one view.
The Sizing Details also reflect the sizing information for all the clusters combined.
Here is same recommendation but for just one cluster. Note just the hardware and the workloads assigned to that cluster is in the view.
The Sizing Details reflect the sizing information just for that cluster.
Alternatively can look at Rack View for All Clusters or on a cluster by cluster basis
Likewise can view Sizing Charts for All Clusters or on a cluster by cluster basis