Pretty much was as stated above in the earlier days of Standby, though depending on the route and the day you could almost be certain of a seat. I was serving in Washington and on our return home in 1979, we flew via Europe. I had read up in the NYT about the ins and outs of flying standby, and worked out that leaving on a Tuesday from Dulles on Pan Am from memory, we could be fairly sure of the 4 seats required to get to London. The flight left around midday, and the checkins opened at 0900, so I drove out early to the airport and waited. There were no people in sight anywhere and eventually at 0900 on the dot a door opened and a bloke came out and opened up his booth. Not only was I able to get the 4 seats for US$65 each, he asked what movies I wanted to see, saying that each part of the 747 had different movies running, so I chose our seats accordingly. Went back to our hotel, collected the family, and returned in time to board for the flight in a not very full aircraft. Used the system a few more times, but never with the outcome on this particular flight.