Putting a leash on your dog is quiet important. Without a leash, your dog maybe difficult to control. Many places that allow dogs require you to put your dog on a leash. Without a leash, your dog can easily run away or may be a danger to others especially kids.
Putting a leash on a dog can be tricky though Some dogs tend to run very fast and may not want to be lead by their human. This may cause agitation on your dog that can lead to temperament issues.
Ceasar Milan, the famous dog whisperer teaches us simple ways of teaching a dog how to wear a leash.