It’s where the principle of the advantage rule in football came from (or was developed from, to be more precise). The FIFA guidance is that on seeing a foul (and dependent on severity, sometimes it’s better management to stop the game immediately to prevent flare-ups) the referee waits 2 or 3 seconds to see how the play develops. If there is a clear advantage, then they raise their arms, palms outstretched. This does not actually mean ‘play on’ - it means ‘play on, advantage’ which is what referees are meant to shout whilst doing it.
J (qualified referee)