Although I am an advocate of 12 weeks, there are so many factors that I believe influence when is the best time to bring home a Yorkie puppy. For a first time Yorkie parent, I believe it is often better to wait until 12 weeks when the puppy is a little less 'fragile.'
The benefits of socialization and maybe some potty training usually come from good breeders. Not all breeders are good about working with their puppies.
My 2nd Yorkie Teddy stayed with his breeder 8 months. I often joke that I would do that again in the future because he was so well trained.
I know a bunch of Yorkies who went to their homes at 8 weeks and they had no problems. Their pet parents are good trainers and know essential care for little ones. When I brought home Max at 13 weeks, I had no idea what I was doing. I'm lucky that he had a good start with the breeder, he was a sturdy 3 pounder, and he is innately a very good boy.