Originally Posted by corporate-wage-slave

Three exceptions:
1) Those with certain mental health issues, and some nervous flyers (of which there are a lot) actively seek out middle / middles. Statistically there is likely to be one or two such passengers on any larger aircraft.
2) Some very large passengers, and others who aren't mobile quickly, prefer middle due to mobility issues and fear the person next to them will need frequent WC breaks
3) Those who genuinely don't greatly care where they sit but do object to being rearranged by someone gaming the system.

And I've done point 3, so beware!