In VMware vSphere environment, why Smaller vCPU is better than Bigger vCPU (if the workloads only require few vCPU) in a fully probable contention environment?
To explain this further let’s take an example of a four pCPU host that has four VMs, three with 1 vCPU and one with 4 vCPUs. At best only the three single vCPU VMs can be scheduled concurrently. In such an instance the 4 vCPU VM would have to wait for all four pCPUs to be idle. In this example the excess vCPUs actually impose scheduling constraints and consequently degrade the VM’s overall performance, typically indicated by low CPU utilization but a high CPU Ready figure.
So, always start with smaller vCPU and then add extra vCPU later on if needed based on your observation about the workload.
This reference post also share a very good description why too many vCPU will give poor performance to your Virtual Machine: http://www.gabesvirtualworld.com/how-too-many-vcpus-can-negatively-affect-your-performance/
Conclusion: “Right Size Your VMs!”