Ebay's give you a second chance facility for 2 reasons.

1) If the winner does not pay then you can offer it to the next highest bidder at the price he bid for it.

2) If you have more than one of the item you have auctioned then you can offer any of the underbidders a chance to buy it at the price they bid at. It saves you having to list items again and you know what price you will be getting.

Plus if the item sells on the second chance offer then no listing fee is charged.