"Whisker poles are used for non-spinnaker class racing and short-handed cruising, or whenever downwind performance is desired without the use of conventional spinnakers. A properly sized and deployed whisker pole will allow the headsail to add considerable power and speed to downwind sailing. Telescoping whisker poles allow one pole to be used with furling headsails or multiple sized jibs and genoas on a given boat.
By projecting the headsail out to weather and out of the mainsail’s "wind shadow", the headsail can fill and stabilize. Without a whisker pole, the headsail will flop from side to side, limp and useless. The use of a whisker pole will allow "wing on wing" sailing dead downwind with surprising performance. In recent years, asymmetrical spinnakers have become "all the rage" in off-the-wind sailing. These sails are subject to the same dynamics as jibs or genoas as you turn closer to dead down wind or try to sail "deep".
The use of a whisker pole to hold out the clew of the asymmetrical sail will stabilize the sail in the same way as it does a genoa and allow better performance and an increased "sailing angle" with these sails.