Strip away all the technical jargon and a virtual machine management package is just a software program, which emulates a real computer for each instance of a virtual machine (VM). So, it will have virtual USB ports, virtual network connections, a virtual processor and so on, each of which will use up resources of the real, 'physical' machine.
Each VM instance will need to run an operating system and whichever applications it requires, as will the physical machine. In principle, it stands to reason that the total load on the physical processor at any moment in time is going to add up to the sum of all the OS'es, applications, device drivers, virtual machine management tools and whatever else is running, whether they are on a physical machine or a virtual machine.
With this in mind, a question we are often asked is whether anti-virus software should be installed on the physical machine, or in each virtual machine instance. At first glance you'd think...