One of the more concerning aspects these days of the pet dog world is the proliferation of 'designer breeds'. You will see advertisements for 'extremely rare' doodle-type 'breeds' (at extortionate prices due to said claimed 'scarcity') where one pedigree dog of a random breed is mated with a standard poodle. The rationale behind this cross-breeding is often stated to be that the resulting cross breed will be 'hypoallergenic' and therefore suitable for people with pet hair/dander allergies. Nothing could be further from the truth.
To understand this you need to consider what actually happens when you mate a male and female dog and what traits will be passed along. In every case the offspring will receive a proportion of their genetic code from one and the remainder from the other parent. If you therefore mate a dog with a long smooth top coat and a furry undercoat to a different dog that actually has continually growing curly hair such as a poodle what will the results be? You simply won't know what the puppies are going to be like because each embryo has a different mix of genes. You may get a curly coated dog with fur and an undercoat or you may get long hair or you may get hair with a curly undercoat or any other combination. Ultimately, the hypoallergenic properties of a dog where it relates to fur and hair are going to be uttlerly unpredictable. People with allergies who want a pet are being deceived by adverts stating that these crossbreed puppies are going to be good for them - so it's not surprising that many of them end up being abandoned or rehomed. If you are allergic to dog fur, but not dog hair, and want a dog with hypoallerginic properties, then get a pure bred dog with hair, don't get a 'designer' cross breed. Do not be deceived by effusive advertisements by those catering to the fad for 'designer' crosses. You are being conned.
Closer to our home, if we imagine crossing a setter with a poodle, we envisage puppies with utterly unmanageable coats. Those of us who have in our homes a spayed or neutered setter will understand how that can frequently ruin that dog's coat. The formerly flowing smooth locks that give the setter its popular and graceful experience often turn to tight straw-like curls that will knot and matt as soon as that dog just looks at you. Without constant care and attention, those matts can end up inhibiting movement and causing that dog discomfort. Why would you deliberately breed a dog that is going to cause years of heartache and discomfort for both of you? It's quite simply cruel.
In the same way that you cannot predict a 'doodle' cross's coat type, you can't predict the temperament qualities of that cross either. Dogs have been bred for centuries to accentuate specific temperaments, instincts and activity types. Some dogs are bred for scent work, others are sight hounds, others set on encountering types of animals they are bred to hunt, still others are bred for aggression and protective qualities, whereas others are bred for intependent free ranging and others are bred to bond instinctively to one master or a group of people. What are you going to get when you cross a breed with a certain set of instinctive qualities with another with a totally different set? The answer, need I have to say it, is... you have not a clue. You may get a combination of temperamental traits that work or you may get a dog from hell who simply can't be trained for your environment. If you want a dog to fill a specific role, then look up the breeds you like the look of and find out whether their temperaments and general breed history fit in with what you are expecting.
For instance... we're explicitly interested in the setter breeds. Temperamentally they are extremely loveable, very intelligent, they adore their owners and yet they have minds of their own. They would be hopeless at herding sheep however. No farmer would ever use a setter for that purpose. If you want a dog that craves human company and will stick to you like your shadow, find a breed that does that: with a setter you'll have endless entertainment, but be prepared for a dog that will range far and wide in the park when off the lead.
There is an old-wives tale that cross breeds are naturally healthier than pure bred dogs. This is codswallop when relating to the current fad for 'designer dogs'. The vast majority of them are churned out by inconsiderate breeders who have no interest in breed health and reguarly ignore the testing required in the individual pedigree breeds to ensure the potential mates aren't carrying anything dangerous. Additionally these unethical breeders frequently have no concept of the genetic dangers inherent in crossing one type of breed with another. For example, we have heard of cases where English Setters have been crossed with Merle Border Collies. If you have any knowledge of Collies, you know that you NEVER mate two collies together who carry the merle gene since this frequently results in birth deformities, deafness, blindness, etc. What these people do not consider is that the English Setter, by reason of the genes that affect the type of coat colouring, is also at risk of these deformities when crossed with a Collie. In these and other breeds, the unethical types carrying out these crosses give no consideration to these outcomes: they're breeding for money and nothing else, and they're doing it regularly because of a fad built up around ignorance in the general public about these risks.
Committed and ethical breeders test their dogs for all the genetic conditions that are risks for their chosen breed. Those that are found to be affected by a condition are removed from the breeding pool. Those that are found to be carriers are bred from only if there is a reason to do so and are only bred to other dogs that are demonstrably clear of that condition so that no offspring can ever be affected. They endorse their pedigrees to ensure that no offspring can be registered until and unless they have they healthchecks satisfactorily completed. You won't get that from a 'designer dog' - simply because such dogs are completely untraceable and unregistered. Do you know that dog's background? Can you research the parentage? Not easily.
'Designer dogs' may be popular but they're unwise. Litters of these crossbreeds will contain a range of traits and, contrary to the misleading adverts you will read for them, what you will end up with in an adult dog is almost entirely unpredictable and may end up in a situation that causes you immense heartbreak.
Do the sensible thing. Research the pedigree breeds, find the traits that matter most to you in the breed that appeals most to you and find a breeder who mates their dogs responsibly, carefully and who conducts themselves in an unimpeachably ethical way. Never ever buy a 'designer dog'. The only thing about it that is by design is the lack of ethics of the breeder.