Old Vermin's picture is of a ceilidh in a marquee. That can be very unfriendly for acoustic instruments - canvas just seems to eat sound. But feet on flattened grass or wood chippings are at least quiet.

I have played for a wedding in a marquee with just me (recorders, whistles, flute) and a harp. It worked, just. We stuck to very familiar dances that didn't need calling. It felt like we had to throw every note like a pebble at the furthest-away dancer.