Actually, if you neuter before the growth plates close, it can delay the closure and the long bones can grow longer, which will lead to a leggy dog, depending on how early with respect to the individual -- when that individual would have reached his adult height. If all GSDs grew at the same rate, reached adult height at say 18 months, then easy, neuter at 20 months and all is good.
The problem is that they grow at different rates.
If someone isn't breeding for oversized dogs, and I mean dogs that are well over 100#, if they are breeding dogs within, or slightly outside of the standard, they can still produce a larger than standard dog, but generally not a dog that is 120#. Which means one of two things is going on. People are deliberately breeding dogs that are grossly oversized to create puppies that will also be, or people are allowing dogs that should be 90 pounds to weigh in at 120. Both of these are just not good, and likely to cause health problems, and both will impede the ability to do the job, one because obesity causes fatigue, injury, and illness; and the other because people who breed for one aspect that is totally outside of the standard, are probably doing so with less or no regard to other important aspects.
There is a section in Farmer Boy, where the father and son are at the fair looking at the horses. The father greatly admires the huge draft horse that someone brought to the fair, saying, "it could pull a barn." The boy who is 8 or 9 years old, says something to the effect, why would we want it to pull a barn, the Morgan can be ridden or driven (paraphrasing here), The father agrees with him, and that it would be a waste to feed all that muscle that is simply not needed.
The German Shepherd Dog needs to be large enough to move the sheep, and to guard the sheep, quick enough to move the sheep, agile enough to move the sheep, beyond that, is a waste of feed, to the poor farmers/shepherds in Germany.
We skip over to police/military work, without which, our breed may have had a short history. The dog has to be large enough to give criminals pause. But if police wanted larger dogs, they wouldn't be moving to Malinois, which are a bit smaller and thinner than GSDs. It is funny, buy my little Babs, who seems small to me, but weighs in between 68 and 72 pounds, actually makes full-grown men nervous. Weird. Maybe it's the upright ears.
Why would you want a 130# dog when a 68 pound bitch backs up adult males?
Now, I have a pup who is 8 months old and 72 pounds. He has huge paws, and I am afraid he will continue to grow, and may break 100. I hope not. How will I pick him up if he hurts himself and I have to lift him into the car. So far, I have been able to manage dogs weighing up to 90 pounds.
I guess I just don't understand the desire for dogs that are grossly over what the standard dictates for the breed. If you get a lean, 100# dog, don't kill him, kind of embarrassing from a breeding perspective, but certainly loveable and will most likely make a great pet. Going out of our way looking for breeder who breed for dogs that are typically over 100#s is encouraging that type of breeding. You have to spend more for food at the minimum, and they do not have 30% more personality than a properly sized dog. Get a leonberger or a mastiff if you want a giant dog. It's not right to build shepherds to double their size because we like them big. It would be like wanting a Chihuahua-sized GSD, and breeding down, down, down to get one. And then when we end up with a 7 pound GSD, being so proud of it, and finding breeders who make the smallest dogs.
Just today at Tractor Supply, I am giving people the thumbs up on Diamond Naturals, of course, I find the two people in the store that have GSDs, and the one's dog is imported and 130#. I thought super-sizing the GSD was an American thing. Guess not.
At some point, we really need to ask ourselves, why? Should we make one with no coat so that people who are allergic and want a hairless GSD will be satisfied? When do we say, this is what the dog is supposed to be, and stick with it?