Utilizing VMs relates to power consumption specifically because aggregating a physical machine into a virtual one reduces power consumption. Why pay for idle CPU cycles on two machines when one will suffice? If both machines are being utilized you have an excellent argument to keep them both, but it falls apart when the machines are largely idle. We're in the scope of the lazy weekend sysadmin at home, so of course these machines all run only sporadically.
As for multiple human bodies using a machine simultaneously - of course you are correct only one physical human can access the GUI of a machine at a time. But between network access and the time honored tradition of "waiting" and "sharing", it's pretty reasonable for 2 or even 3 people to maintain separate user profiles on a system and just swap between them.
Even that said, it's completely realistic on Linux systems to supply an additional video card, assign a different session ID to it, and have two monitors, two keyboards, and two mice, all working simultaneously and without regard for the other. I've seen community libraries with 4 of these on a single computer.