A couple of months ago on BCN-ZRH flt,I asked the nice lady at check in for a window seat. She gave me the window seat on the back row of an MD80. ie view obliterated by the engine. However on board the Iberia MD80, one of the window exit rows was completely empty. Cabin crew, asked if I would mind moving forward to the exit & drew my attention to the required safety brief.
Well done Iberia
I've quiet often been on flights ( various airlines)were the exit rows have been empty, however, it's not usually long before there's a scrum trying to bag the seats. The danger is, someone completely unsuitable sits there, then it depends on how bothered the cabin crew are, this is a bit of a lottery. It SHOULD be a much higher priority at check-in to sort these things out in advance.