Inbreeding is the practice of mating animals closely related to each other, and it is used to preserve and intensify desirable characteristics. By mating two dogs from one bloodline, you increase the chance of their puppies having their characteristics. Take a look at the pedigree of most champion dogs - you will see the same ancestor mentioned several times.
However, although inbreeding certainly has advantages, it has its disadvantages also. Serious faults and blemishes are inherited twice as frequently as they would be if the dogs were bred to animals without these faults. Also, breeding between animals that are closely related can lead to physical weakness, bad temperament and less intelligence in the puppies. Use inbreeding with care.