This keeps your shoulder from hurting when you are playing ball with a dog that will never give up.  It helps throw a good distance with out hurting yourself.  You just need a big yard or dog park to play with this.  This comes with the chuckit! tennis ball but I prefer to use the chuckit! rubber balls they last longer and bounce higher and goes in different directions.  I have tried other ball launchers and by far this is the best one to wear out your dog and keep you from not working to hard or hurting yourself.