From SLF point of view, having flown most flavours of loco, there doesn't seem to be any difference in the time taken to actually board the aircraft, whether seats allocated or not. Locos out here, such as Jetstar Asia and Tiger Airways, use allocated seating. This is done using a laptop computer and small portable printer, the boarding pass is a flimsy piece of paper similar to some credit card receipts. There may be a small discussion at checkin if someone wants to sit with someone else, but nothing compared to the luggage repacking scrummage and dirty great long queues that are experienced at Stansted.
It's little things like this that enable the passengers to kid themselves for a moment that they might be flying a more expensive airline. Can't be a bad thing for the loco, at minimal cost.