Originally Posted by
xyzzy
"There are many jobs where the risk to a lone worker is deemed so high that two people must be present."
protecting the safety of the worker
Or the consequences of any thing happening to that worker. I was not limiting my comment to the issues you cited.
Take a simple emergency, say fumes in cockpit. The PNF, or other suitably qualified person can start the actions without having to fly the aircraft.
PS, as an aside, how many times do pilots in a 2-man cockpit practice single man operation in the simulator?