When the wind drops to 6 knots or less the surface of the boundary between the water and air does something interesting to the wind. The interface between the wind and water surface creates friction because of the laminar nature of airflow at the velocity. What this means is there is more wind shear at this boundary layer of a few feet above the water surface.

In other words when a light puff of wind moves across the pond, it will drag against the water's surface (friction) and slow down. Mean while the puff that is moving higher above the water's surface will move faster (less friction). This will cause a difference in wind speed for a given puff and interesting boat handling.

Let's say you are sailing along in light air and a weak puff is moving towards your boat. Because of the water's surface friction, the puff's upper airflow will hit your upper sails first before it hits the lower bottom of the sails. This will cause your sailboat to do a quick heal thus loosing boatspeed, until the boat recovers. When this happens, let your sails out a little to allow the wind to fall off at the upper level on the sails - it is like putting in extra twist without you being there to do it. Then when the boat gets underway you can bring in the sails and off you go.