It depends on the individual dog. In some instances, a dog might feel more comfortable snuggled up to his owner. However, carrying a dog in a backpack involves restraining the dog to a small space and/or putting him/her in an unusual position (especially if it is a legs out backpack). Generally, dogs are more cooperative than cats and will tolerate these things fairly well, but dogs who are healthy and love to run free probably will not be so comfortable in a backpack.