[yorkietalkjilly]

Since Yorkies carry their tail out in back rather than curled protectively over the back and it is a thin tail, even at its base, in the early days of the breed they were apparently often injured via laceration/fracture/frostbite and animal bites on them as the dogs engaged in rough play and generally pursued their activities around the farms and mills of the area where they were developed as a breed. Homes/farms of old often had many large dogs, cats and other critters living on the property with the small Yorkie, as well as plenty of rough people and the little dogs frequently lived outside and slept in barns, even in the coldest spells of weather. There were few fences than so they dogs would run where they wished and get into whatever trouble was available.

Today, the dogs are no less prey-driven to chase anything running from them through whatever lawn furniture, child's bicycle, small openings or other barriers might be in the way and are still as impulsive as they were back then. Though they aren't chasing rats through snaggled wooden barn walls, they do find troubles for their undocked tails from time to time due to its size and carriage.

Still, I think the reason most breeders dock/have them docked is to conform to the standard and for the compact look of the dog.

I personally prefer the look and convenience of an undocked tail, not ever having to worry about Tibbe getting his caught in the door or things like that, terriers being the impulsive creatures that they are.