On my last flight with Ryanair last weekend there were several empty exit rows, because the FA refused people without reservation to sit there. After completing boarding she was looking for healthy young men to reseat them in the window exit row seats.

I think booking the XL-Seats when flying Ryanair is the best deal in the air. For 10 Euros I get a lot of extra legroom. High chance of an empty row, as they block everyone without reservation. And I can skip the (often long) line at the boarding gate.