Inbreeding is a frequent debate topic among breeders. The ones who defend it and use it, more or less tightly and sistematically, praise how quickly good results can be achieved as far as morphology is concerned, because it allows to fix desirable traits and homogenize type. The drawback is unwillingly fixing negative traits caused by recessive genetic mutations - for which all living beings are carriers, in spite of not showing them in their phenotype.
Those recessive genes might be responsible for innocuous faults (such as too much white on their coat) but also for serious, disabling hereditary diseases. Given the recessive nature of those genes, a dog carrying only one copy (allele), inherited from one of his parents, will never develop that disease and, if no genetic tests are available, his owner might never know he's a carrier for that allele. However, if that dog is inbred to his mother or a daughter or even linebred to a grandmother or grandaughter/ greatgranddaughter, the odds for that bitch to be a carrier for the same allele are very high, thus leading to a 25-some-odd percent of the progeny inheriting two recessive alleles (one from each parent) and becoming affected by that problem.
Some breeders who defend inbreeding are aware of this and use that practise as a means to test the genetic makeup of their dogs; if some puppies from one of their litters are diagnosed with a serious inherited recessive disorder, those breeders will then learn that both parents are carriers for the allele responsible for the problem and cast them off breeding. That test litter will provide the informed breeders with more knowledge about their lines' genetics and might help them control a problem faster than if they worked in outcross. However, the price to pay will be too high: some of the puppies from such inbred litters might turn out affected by lethal, sub-lethal or disabling diseases. The benefits that test will bring do not justify the suffering the animals and their owners will go through. For us, Ponta da Pinta, bettering the breed cannot be achieved at the expense of the dogs' welfare. An ethical breeding is not an animal experimentation laboratory.