While it would be great not to ever have to use a muzzle, sometimes we just don't have a choice. If your dog is scared of the vets (not uncommon!) it can be great to get him or her accustomed to wearing a muzzle. It means you won't have a fight on your hands when you get there, and the dog could be less stressed as they are not worried about wearing one. It takes time and patience though!
I'll upload another video showing introducing a muzzle using clicker training soon.