Ryanair started off having a complete free-for-all scrum, but nowadays have modified it. You're given a numbered card at check-in, which corresponds to the order in which you checked in (I suppose like a sequence number). This then determines the order in which you board the aircraft. Once aboard, you can sit where you like. So it takes no extra time, but avoids the scrum.
Which is a bit of a bugger for us rushing to Stansted after work, who can still manage a respectable 100m time!!
Not quite sure how it works now with their on-line check-in; haven't flown FR for a year. But my point is that it is possible to have non-assigned seating and still avoid the scrum.