QUOTE(Michelle21 @ Jun 15 2008, 11:01 PM)
You can't go into detail because that's a ridiculous comment to make. A swing is employed to cover various parts (usually ensemble) - they normally only go on if somebody else is off through Illness, Injury or Holiday Etc.
Some shows do have on-stage swings - mainly tours and regional shows rather than West End ones. They're used to pad out crowd scenes and they hang around at the back of ensemble dance numbers. What makes them swings rather than ensemble is that their tracks contain nothing that needs to be taken over by someone else - not a single solo word, not a single solo step - so they can move into another role as required without leaving a gap in the show.
It's uncommon, however, so I think "many a swing I know" was something of an exaggeration.