Our teachers occasionally would make us dance with just that connection. They did that because it was the key connection for many moves and was a way of insuring, I was leading the manuever properly. Sometimes because of congestion, I move my left arm to a position, were it does not help the lead at all ( to fit through a small space ) and we do not have problems because that connection is lost for a period of time.

Emphasising that really helped our smooth dancing. I see a lot of men trying to do way to much with their left hand in smooth.