I was unaware of the linebreeding (or what linebreeding was).
It's a positive way of saying "inbreeding". You'll have a hard time finding a GSD that *isn't* linebred to some degree, unless you breed for example an American Showline dog to an old East German line dog. That would be considered a total outcross, almost like mixing two different breeds.
Linebreeding definitely has its merits when done in an intelligent way. Basically, it concentrates genes, both good and bad. If the same dog appears on both sides of the pedigree, perhaps several times, you have to take a look at that dog. If it is an excellent working dog, rated excellent in conformation, with a good solid temperament and good hips, that linebreeding is generally regarded as a good thing. There's a lot more to it than that, but for the sake of simplifying things, that's the idea behind it.
However, you have to know what potentially "bad" genes are hiding in the pedigree. You might not want to linebreed on a dog that is known for passing on bad hips, for example. And if you linebreed heavily on dogs that are, for example, known to be sharp, you need to balance it out in some way by also bringing in dogs that have very strong nerves and high thresholds for aggressive behavior.
Hope that all makes sense.