I once broached the subject with my GF about the possibility arising that we might get awards to the same destination on different airlines (due to availability issues), or perhaps by booking one award and one paid ticket, with the goal being to arrive at the destination as close as possible.

The reaction from my GF was as if I had suggested taking separate vacations! She not only wants to be on the same plane, but wants to sit together. Another couple I know, however, occasionally does what I suggested. But not us: I have my marching orders when planning joint travel to get adjacent seats on the same plane, even when we do separate PNRs. I tend to book early so we have always been successful.