Would make sense. If something happened to the original crew, you need to have more crews ready and already trained.

Every Apollo mission had a primary crew and a backup crew (which was usually also the primary crew of a future mission). Apollo 13 famously swapped one of their primary crew, Ken Mattingly, for backup Jack Swigert because of a risk that Mattingly had contracted rubella. Mattingly was in good health, however, which allowed him to help NASA figure out how to keep the astronauts alive after the failure of the service module.

Ironically Apollo 13 was the final spaceflight for all three of its crew but Mattingly went on to fly on Apollo 16 and a couple shuttle missions.