If you go somewhere a festival is taking place for the purpose of playing in sessions with other musicians who wouldn't be there if it wasn't for the festival then surely you have a moral obligation to make a financial contribution to the festival. Otherwise you might find it won't be there next year. That's what I meant by putting the festival in jeopardy.

There have been a number of festivals which have been cancelled not because they had lost money but because advance ticket sales weren't good enough and the organisers felt they couldn't take the risk.