I don't think in the case of the session I'm talking about there's any conscious desire to play fast. But when the beer's flowing and the crack's good and onlookers yelping encouragement, then the speed and the volume increase inexorably!

I agree that it isn't always to the benefit of the music - but then again the session isn't always just about the music, it's about the crack, the slagging, the buzz, the opportunity to give new tunes an airing, etc.

Unfortunately as well as punishing the music, this type of event can - as my case illustrates - punish the players as well!