Not in the sense of running out of machines, but at least from my past experiences if your VMs share physical hardware with someone who is using their maximum I

Not in the sense of running out of machines, but at least from my past experiences if your VMs share physical hardware with someone who is using their maximum IO, yours will suffer as well. It makes it more challenging to load test. When there is no contention you can usually 'burst' to use more of the machine's resources, but you can't necessarily trust that you will always have that capacity.