I visited recently a dog owner who couldn’t control his dog while walking. Their walk was more a “dog walks man” than “man walks dog”. You know what I mean. This kind of pulling the leash wouldn’t be so painful for the dog if he had a dog harness. But well, just having a dog harness doesn’t solve the pulling-the-leash problem.
A dog harness is nevertheless the better solution for any overly energetic dog than a simple leash or even a retractable leash. It is holding the body of the dog instead just his neck and feels definitely more comfortable for the dog.