Today I read that dogs are twice as likely to threaten other dogs when they are on a leash. This is probably true. I think if you were going to get in a fight, you would prefer not to be tied down. Think of how the dog feels. Other dogs are sometimes aggressive and when your dog is on a leash, that puts it at a disadvantage in a dog fight. Even so, the law says you must keep your dog under control at all times, so keep it on a leash.