Ideally, of course.
I recently booked a 77W on JFK-LHR maybe a few days before departure and the windows were all booked. I set a seat alert for any open window and of course the only one that ever opened was in row 5 right behind the galley. No thanks.

But I did figure that the recessed head area probably meant the seat was private enough (I had only been on this seat before in a window), so I was probably fine with a center seat for a redeye.

Of course due to a 2.5+ hour maintenance-related delay, I switched to a BA flight, and naturally at the last minute the only available seat in J there was one of the dreaded center "lovebird" seats. That was kind of awful. Not only is there ZERO accessible storage when you're reclined/in bed mode, but you're RIGHT NEXT TO your neighbor. There is a privacy screen that slides out a little bit, so it wasn't the WORST thing in the world, but it was still pretty pathetic for a modern day business class offering.