Line breeding is:
A breeders tool used to develop, isolate and set specific desirable traits into succeeding generations. Line breeding can be seen in registered dogs by having specific high caliber or quality ancestors two or more times in the recent pedigree as noted in the table above. Line breeding often has more than one high quality ancestor multiple times in the same pedigree. However, from a purely scientific point of view, linebreeding can also be defined as breeding two individuals containing at least one common ancestor. This common ancestor may contribute a negligible amount to the descendants, or a great amount. This makes the scientific meaning lacking in true art and practice. You can do a line-breeding that has absolutely nothing to do with refining or setting specific traits or you can practice the art and craft of breeding better animals and make rational choices in your program.
Ultimately, linebreeding is simple concept that is extremely complicated as a breeding tool. One must remember that linebreeding is a program that produces animals from a single line of descent from a common or a few common and outstanding ancestors. The goal is not to reproduce the quality of the ancestors but to try maintain as many of their good qualities as possible while improving their deficiencies by refining the genetics of the line. If you know a breeder that is producing the perfect animals then why the hell do you need to breed? Just buy all your dogs from this breeder. If a breeder is producing superior dogs and you breed off their lines will you produce better dogs than that breeder? If not then do the breed a favor and do not breed.