Working purposes: For some working dogs, having a docked tail was practical and even necessary for their specific job. For instance, when certain hunting dogs were chasing prey through dense undergrowth, a long tail could be an entanglement risk. Docking the tail reduced this hazard, allowing the dog to move more effectively. Some herding dogs' tails were also docked to prevent injury during their work, such as when moving livestock.
Preventing disease: Many years ago, there were folk traditions that docking a dog's tail could help prevent or cure various illnesses, including rabies. There was no scientific basis for this belief.
Preventing injuries: In the past, dogs were commonly used for fighting, and some people would dock the tails of their fighting dogs to prevent their opponents from grabbing the tail as a means to gain an advantage in a fight.
Aesthetic preferences: Some people preferred the look of dogs with docked tails and viewed it as a desirable cosmetic alteration.
Breed Standards: In dog shows, certain breed standards have traditionally emphasized a docked tail as part of the breed's appearance, particularly for specific hunting, working, and sporting dog breeds.
However, it's worth noting that docking tails is considered an unnecessary practice by many animal welfare organizations today. It's increasingly seen as cruel and unnecessary, and many countries now have laws and regulations that restrict or prohibit the practice of docking without a valid medical reason. Tail docking is now primarily performed for aesthetic reasons in very few countries.