There are some tips you can give to your customers and policies you can set to keep things simple. For a start, keep the building blocks simple—one VM, one OS, one application, and one instance. So, avoid having one OS running the web, app, and DB server or avoid having one Microsoft SQL server running five instances of databases. The workload can become harder to predict as you cannot isolate them. It is recommended to adjust the size of the peak workload for a production environment. A month-end VM needs to be sized based on the month-end workload. For a non-production environment, you may want to tell the application team to opt for a smaller VM, because the vSphere Cluster where the VM is running is oversubscribed. The large VM may not get the CPU it asks for if it asks for too many.

Be careful with those VMs that have two distinct peaks: one for CPU resources and another one for memory resources. I have seen this with a telecommunications client...