I'm a mature (cough-cough) 65 now, but for some reason being "told and/or ordered" to switch brings out the "you're-not-the-boss-of-ME" syndrome. Being "asked" to switch for a good reason, now, brings out the grandmother in me who wants everyone to be happy.

I like to sit next to my wife on long flights also because I don't have to be so vigilant about remaining somewhat frozen to avoid encroaching into the seats next to me - I have a large frame so it can be a problem depending on the seat width and pitch. On our last flight back from the states we got the typical "Would you mind moving so we can sit together?" I immediately answer that no, sorry, we won't move. My wife then says, "You're so mean! Of course I'll move." She moves across the aisle and later I see her sleeping like a log!

I like to eat, even the crappy food served by some airlines. I prefer to sit next to my wife so I can try her food. If she orders a chicken dish then I order a beef dish so that I can try both. She rarely finishes her food so if she sat next to me, it makes it easier to eat her stuff. I don't need to sit next her but if someone else sits next to me, that person's food might disappear. :-)

It is more natural to sit with one's travel companions. If you are together, you can to some extent shape your environment, and reduce the risk of being crammed into a seat next to some overweight [person].

Yup. My wife and I almost always share things off our trays.

A related question: different flights
 

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.

First time I was asked to switch seats in AA F a few weeks ago. Since I was travelling by myself, I said since it was the same row as well and I wasn't losing out on FEBO. Don't know why they asked even though they didn't talk to each other the entire flight. The seat condition of my new seat wasn't the greatest too but nothing major..

As long as I don't get last choice on meals, have less pitch, or have a big seatmate then I would consider it as long as I'm travelling by myself as well.