If I ask you why you want a Lhasa Apso, a Golden Retriever, A Sheltie, or a German Shepherd or whatever breed you have chosen  I can naturally assume that it is one that you like the looks and size of... but  I would bet you're going to talk more about  their  personality;  how much they like kids, how good of a guard dog / running partner/lap dog/hunter  they will be, how they will interact with your other pets ... 
The things you will be looking for aren't the things that describe just "dog"; they'll be the things that make this particular breed unique .
That's where people have made the right initial decision – they've made the effort to understand that there are differences between breeds and that they should get one that  comes close to matching their picture of what they want a dog to be.   Only you know how much time and energy you have to dedicate to grooming, exercising and training a new dog. Only you know what the needs of your lifestyle and family are --- a good breeder will ask you questions and try to help match you to the right individual dog or puppy they have available; or refer you to a different breeder or maybe even suggest a different breed !
Too often the next step people take is to  go out and find a dog of that breed for as little money and with as much ease as possible. Maybe they  don't want to pay the high price they think a breeder charges, or they don't think they need a "show dog" or they want one of the sweet little puppies the neighbors across the street have.  Maybe they don't want to go through the interview process many breeders require before placing a puppy. Or they simply think they are getting a real bargain  because they can get a Lab for $300 or a Shepherd for $150.
Those things that distinguish the breed you want from the generic world of "dog" are only there because people have worked really hard for multiple generations to get and keep them there; and as soon as that work ceases, the dog, no matter how purebred, begins to revert to the generic. That doesn't mean you won't get a good dog – the magic  of dogs is that even the most poorly bred one can still be a great dog with a keen mind and loving soul – but it  will not be a good Shepherd, or good Lhasa, a good  Golden, a good  Sheltie or a good  Aussie ---  You will not get the specialized abilities, tendencies, or talents of the breed.
Keeping a group of dogs looking and acting like their breed is hard, HARD work. Show puppies and pet puppies come from the same litter with the same parents and pedigree. The same amount of care has gone into planning the breeding, doing health screenings on the parents and  watching over the mother dog during her pregnancy and birth. The same amount of time and money is invested in food and vet expenses. ALL the puppies are loved and socialized and well cared for . Many "pet" puppies could in fact be shown because of  the level of quality and soundness that  exists in the entire litter ! Helping someone take the first step in forming that special bond between a dog and it's owner , whether it will be shown or not, is one of the greatest joys of raising dogs.  There is no such thing as "just a pet" !

I want you to not only realize the benefits of buying a show-bred dog,
 I want you to INSIST on a show-bred dog. And then when your workmate says she's getting a puppy because her neighbor will give her one for free, or when your brother-in-law announces that they're buying a goldendoodle for the kids,  go steal their wallets and their car keys ! 

If you don't NEED those special abilities or the predictability of a particular breed, you should not be buying a dog at all. You should go rescue one. That way you're saving a life and not putting money in pockets where it does not belong.

And, above all else, PLEASE  remember that all puppies are cute! Do not impulse buy! That adorable ball of fluff IS GOING TO GROW UP! 

When you buy a puppy at a petstore,
 you are atleast the third home its been in during it's young life! 
Buy from a reputable breeder!  Know what kind of environment it lived in after it was born, and how the mother is  cared for !