My job as TIC or FIC (third or fourth in command) is to sit in the left seat so the PIC can go take a nap. We 777 FO's are fully typed and trained in both seats. I fly as SIC/TIC/FIC, but can sit in any seat during the flight. The PIC sits in the left for takeoff and landing (company says so), but anyone could since we are all trained and certified to.
I think the answer to your question involes asking more questions. What type of plane? What type of flying? Is it a 2-pilot airplane? What is the companies policy? What does the insurance company say?