Ryanair have a policy of deliberately splitting up passengers who book flights together, unless one is prepared to pay a fee for specific seats. My family have travelled several times with this unfortunate carrier in the last few weeks.
What tends to happen is that there is some 'seat swapping', and not just a row or adjacent seat, but passengers moving from one part of the plane to another. Groups booked together want to sit together.
On arrival, this causes delay as these displaced passengers are likely separated from their cabin baggage, and trying to go against the flow of leaving passengers.
It struck me, observing the melee, that in an evacuation procedure, it would only take a tiny minority of these many displaced passengers to go for their hand baggage to seriously compromise the chances of getting out. There is good probability that some passengers will always ignore the instructions and try and take hand baggage in an evacuation. Perhaps Ryanair's policy here is actually starting to compromise safety?