There are many reasons why people would mix breed dog's. Some people are just curios to see how there dog will turn out. Another reason why people would mix breed a dog  is to  create a dog with certain trait from each parents But it takes generation after generation and more than one pair of dogs with the same traits  to achieve a dog with the traits that you want. Mix breeds usally have 50 percent of the genes from both parents, so there is a 50/50 chance that the traits can be either good or bad. Many people dislike mixbreed dogs because they can be unprdictable either health wise or tempermant. It can be hard to predict how a mix breed puppy will turn out. Dog's have been breed to have specific skills like gaurding, sheep herding, retreiving and sheep herding. Some people feel by mix breeding you take away the desired traits that people worked so hard to get breeding dogs generation after generation. Although many people disagree with mix breeding because of some negative effects the results can be positive if done correctly with dogs with dogs who have no history of major healths problems. Remember if you do decide on creating your own breed of dog make sure both parents have a clean bill of health and know your dogs bloodline and any major health concerns.