I too love the look of the long hair on a Yorkie. It's a true normal look and very beautiful! "However", my Azrael has a true cotton coat and it is extremely thick. (Enough hair for four dogs) It's a horrible mess to keep the matts out despite having to brush and comb twice daily and use lots of conditioner and grooming spray. It isn't fun for her or me, so I cut her short, not shaved.
My youngest, Razael (2 1/2 years old) has a thinner silky coat, and has never had a hair cut. It's long to the floor. I do have to keep her underside cut short due to those tiny matts that collect there, like under the arms, groin and tummy. I do brush her every morning to keep the coat from any matts. Zada has a beautiful thick but silky coat and for some reason I don't have much of a matting problem with her. She also gets a morning brushing without fail.