The rationale behind letting the navigators unofficially become familiar with how to fly the airplane stemmed from the possible need for the back-seater to bring the aircraft home in case the pilot was incapacitated, as might occur in combat. So most navigators at least got enough familiarization to maneuver the airplane, fly it from point to point and the like. Some of us got the chance to do more, even to ( in my case ) actually making takeoffs and landings and aerial refueling.
I particularly remember one flight at Bergstrom AFB when we had been making repeated take-offs and landings near then end of a short photo reconnaissance training mission. We had enough gas after the primary part of the flight to spend an hour or so in the traffic pattern. In fact, my pilot and I were taking turns making the landings and take-offs, 'shooting' touch and go landings.
I had just made an especially smooth landing on our next to final approach to a full stop one. My pilot made the final landing and we bounced a bit, making it a fairly rough one. The instructor pilot, monitoring our efforts from the edge of the runway in the mobile control tower, called to us on the radio and adamantly stated that my pilot was not to let the back-seater make landings. He was convinced that the bouncy landing was mine.

When we got to the Operations Desk after the flight for our de-briefing, the instructor was there and really chewed my pilot out for letting me land the airplane. He noted that bouncy landing and said that that was proof that navigators shouldn't be flying the airplane.
We took the criticism quietly and submissively, never letting on that my pilot had actually made the bad landing. We acted duly chastised and agreed to behave in the future.