As sc-bee said, it depends on the condition of the hive (crowded, sparse, strong, weak?) and how many cells (2, 8, 12, more?) compared to the number of bees. Time of year and location might also play into the answer.
Basically if the hive has a high density of bees and a lot of cells for the number of bees and boxes, I would assume they are swarming. If the hive has a low density of bees and few cells for the number of bees and boxes, I would assume they are superseding. If they are swarming and you don't take action you will lose at least half your bees. Action at the point of having cells, is to do a split and make sure the resultant splits have room in the brood nest. If they are superseding and you don't take action they will raise the new queen, replace the old one and odds are good they will do fine. If they are superseding and you do something foolish like destroy the queen cells, they may be doomed to failure when the current queen finally fails.http://www.bushfarms.com/beesswarmcontrol.htm#supersedure