If the flight is oversold and the o.p. does not OLCI, doesn't the o.p. run the risk that the seat with which he is "reasonably happy" will taken by someone else and he end up without an u****de AND a bad seat?
Last fall a had a space available u****de on my PNR (that flight was also a very full flight). I OLCI and when I arrived at the airport, I pointed out the notation to the agent who took care of the u****de.