The only downside I can think of is if you have 2 QVS servers clustered and if you Pre-load option enabled on the dashboard, it will pre-load on both the servers.
on the Flip side you can restrict the dashboard onto only one node that way it will not occupy the memory on both the servers but their will not be any failover.
You can run the Cluster and set for each document where it should be available and make sure with preload ensure that the document is loaded on a specific node as long both nodes are running. If one goes done, the app will also be loaded on the second one.
In this case you have on License Management for the Cluster. This is a common way to run a cluster.