It is a very old and culturally based tradition. Over the years it has changed dramatically especially in the more urban areas. My father in law on Christmas Eve would prepared a large roast just for that purpose. When and if any mummers did show up they would more than likely been on the go for several hours, he would give them a shot of grog ( rum) a slice of bread and a piece of meat before they went on to their next house. As Todd already said they mostly visit family and the receivers are usually expecting the visit. It is customary that at least one mummer show their face before entering any houses.