Dog snobs seeking the reflected glory (AKA the Association fallacy) of the term "purebred" will seek out a pup which conforms to physical characteristics.
While there is a place for dog conformation (physical and temperament) when you intend the dog for a particular kind of work, the conformation pet owners should be seeking is health, size and temperament/energy level appropriate to social setting and owner lifestyle.
Just one outcross every few generations will allow the informed and responsible breeder to keep a dog looking like a purebred but with the health benefits of increased genetic diversity. This assumes that keeping a dog looking like a purebred is compatible with improved health. Some breeds have been bred to perpetuate deformities that create health problems. Think the short snout of bull dogs and pugs or the hips of some German Shepherds.
Much conformity, however, is type A humans run amok. Sparta is a non-AKC breed but the dog snobs wouldn't care for her, she has some white hair out of place. You know what, I'll take a half dozen white hairs on her back when it comes with improved health and vigor.
Stoic is, at best guess, a Boston Terrier cross and he is perfect terrier-type for an apartment, city life, or, as in his case, for little girl to dress up on Saturday morning and for her dad to take into the field on Sunday..
Musket is a Parson Terrier/Mountain Cur cross: best overall hunting dog I have ever owned. If I'd discovered tracking earlier, he'd have blown the competition away and we'd have been legends in the blood tracking community.
Maybelle, she is all ditch hound, and never have children had such a calm and protective companion.
Out-crossing not only improves health, it need not impact the other qualities of a good pet. It will also give you a unique "first friend."