I was shocked when my friend told me about the chaos he experienced when watching Godzilla on IMAX in USA.
I don't think there's ever been unassigned seating in Sweden. Personally, I would go to the cinema like never if I couldn't reserve spots.
I say this as someone who goes to the cinema around five times a month. I just pay on the website, get to the cinema 10 minutes before the commercials starts, pick up the tickets in the machine, buy popcorn and then just walk in.
A couple of weeks ago, I managed to buy a row of tickets for Dr Strange, 10 people, for all my friends. I paid beforehand and people gave me cash on the spot. We got in, one man was in one of our seats, we showed him the tickets, and he apologized and moved to the row above.
First come, first serve is ridiculous with these kinds of events. It's better to reserve a ticket, knowing that you will be able to sit with your friends, rather than coming into the theatre and having to split up.
Just book earlier, geez.
Also, this reminds me of the thread with the guy who was angry that he would never get a hair cut because he refused to make an appointment with his hair dresser.