Teaching your dog to be comfortable wearing a muzzle is a good idea for a number of reasons. One of them is safety on a hike: if you don't trust your dog 100% around dogs, critters, people etc., having her wear a muzzle will help you relax. If your dog doesn't like strange dogs invading her personal space, but you would like to take her hiking in places where you will occasionally encounter off-leash dogs, having her in a muzzle keeps everyone safe. (Having her on a leash doesn't do that, because strange dogs may still run up to her.)
When I have Grit off leash in an area where we might encounter dogs or people, I usually have her wear a muzzle. She is good with dogs who keep out of her way or greet her politely, but she is not the kind of dog who appreciates rambunctious dogs who come barreling up to her.
