What disadvantages in not queueing early to board Ryanair flight?

There is no risk (or negligible risk) of being offloaded.

There is a risk your bag will have to be stowed or put far away from you on the aircraft, which many people find irritating.

I think most people get impatient, nervous or anxious when they see the flight is close to boarding—and simply do not want to sit any more. Either they join a queue or make a queue, or they form into an unsightly mass as close as possible to the gate. If a small number of people do it, then everyone else begins to follow. It is some kind of instinct many people have.

Some people have rather unpleasant terms for this phenomenon ("gate lice" I have heard).

I have traveled with Ryan air so many times (non EU citizen) and this is what i would answer.

1. If you are not EU citizen, you have to stand in queue to get your passport checked, if not you will be denied boarding at the gates.

2. Most ryan air flights are crowded during weekends, so if you board at the end of the queue, either you will have no free seats (forced to pay 10 euro to take priority seats) or no space to put your hand luggage up above.

The only thing i like with ryan air is that you can sit anywhere (seats not alloted), unlike other commercial airlines, where you will need to spend time searching for seats. of course, I would be happy to wait in queue if i could fly for 40 euros or less. If you are flyer with ryan air for the first time, be sure to check your hand luggage within their prescribed dimension limits.