You can learn to play guitar better watching YouTube videos - it doesn't replace practice, it helps inspire and educate by bringing talented practitioners to the world in a way not possible 40 years ago.
Why not surgery?
Otolaryngologist Martin Young writing at KevinMD.com argues that because he has learned so much from watching more experienced surgeons work, peer-reviewed videos might be the wave of the future - obviously a South Korean teenager may be fun to watch play guitar but he is not going to be a source for best surgical practices.