Had a couple of instances where the single pilot/ 2 crew came into play.
First was in a SPIFR S76, for a private operator, and we flew it single pilot. However, when we had occasion to carry members of the royal family, the Powers That Be decreed that we had to have 2 pilots. We found that it actually DECREASED safety, as we tended to chat about things and people from our past, which perhaps doesn't fit into the Sterile Cockpit environment. But their regal uppitinesses survived every time.
Second was an EMS operation, again in an SPIFR machine, a B412 this time. The next machine in the hangar was also an SPIFR B412, a newer model, but that contract required 2 pilots, which meant ATPL, so my measly CPLH meant I couldn't fly that bird. I could safely fly SPIFR, but legally not with a copilot. Weird. No taking into account the 11 years of operating crewed choppers in the military.