I taught formation landings, both day and night, from the backseat of an F-100F for a number of years. I was of the opinion that it was the one maneuver that required the absolute most supervisory attention from the backseat, particularly at night. Students were generally subject to creating problems when they quit flying formation all the way to touchdown, which was a somewhat common response as you crossed the threshold. (Night formation landing currency requirements were eventually done away with.)
Then there was always the concern about some kind of hardover prior to gaining nose-tail separation on the rollout.
Then with only single-seat A-7Ds during my time, leading a B course student on their first formation landing was always a time to reflect.....and be ready to push it up and get out of the way.
