Originally Posted by
drewguy
One reason is so you don't then both have to shuffle. Recent flight I had 21D, spouse 21A (21C had alreayd been selected). I sat in 21D. When 21C sat down I asked if he'd be willing to swap sides, which he was. (Both B and E were empty)
Had I just sat in 21C there would have been zero inconvenience to him or me having to move, and we would have ended up with same result.
While I did what I did lest I encounter a "you poach, you move" person, there's an argument for preemptively initiating an even swap of this sort. (I would not make this point over window/aisle or any row switch.)
This is clearly a like for like, most people are probably willing to swap.
But the OP's
example was window seats on either side are also "like for like", which I found odd as the sun doesn't shine on both sides equally and I choose my seat to avoid having the sun in my face.