Claws trimming for GSDs can be considered as indicator of their activity level. If you ever have to trim your GSD claws, it means your dog does not get enough exercise. If your GSD has plenty of outside time, when he can run, walk, and jump his claws will be filed off naturally at the same rate as they grow. If claws are growing out to the point you can hear them clicking on your hardwood floor, or even worse to the point of curling at the tips, your GSD needs more active time.
Also, please, consider that you walking or even jogging with your dog on the leash is exercise for you, but not for your GSD. Your GSD can run with the speed 30 mph, so make sure to let your dog run off leash, chase sticks or balls, hunting down squirrels or whistle pigs (small chance of catching them, but a lot of fun and exercise). Good exercise for GSD is to follow bicycle or ATV, but make sure to make pit stops and hydrate your dog.