It makes a person appear snobish by counting people in line and trading places just so you don't have to partner up with a particular person. Mixers are suppose to be the luck of the draw, we all started out as a novice. If you REALLY don't want to dance with someone move to the back of the line.
If no one is standing in line when the guy brings the girl back to the pickup/drop off area a NICE man will ask the girl if she wishes to go around again or stop an wait.
At times 2 guys may end up at the front of the line. At that time the girl/guy may defer to whom ever has not yet danced with the lady.