The reason why some dog breeds have whip tails is similar to the reason dogs have tails in the first place.
An animal will wag its tail eagerly to show excitement or tuck it between its legs when scared or uncomfortable.
A dogs tail does more than serve as a means of communication it also contributes to the breeds natural characteristics.
Sighthounds like Greyhounds Whippets and Wolfhounds have long narrow tails that act as air rudders and help the dogs maintain their balance and stability at high speeds while running.
While running after vermin at high speeds this whipped tail also acts as a brake. Sled dogs such as Siberian Huskies and Alaskan Malamutes have thick and plumed tails that enable them to withstand extreme weather conditions while hauling heavy freight.
The majority of dogs with whiptails are hunting dogs including many sighthounds and scenthounds. Breeds of dogs such as these are suited to visual acuity and speed.
Besides having amazing eye-sight for fast-moving objects like animals they hunt they have long lean legs and powerful bodies for running at Their fast speed allows them to chase down prey while maintaining balance throughout the chase.