I'm with Endiku. GSDs are smart, and they very quickly learn that if they hold out for a meal or a day or two something even better will show up. Unless your dog is clinically underweight, he's just playing you. Both my GSDs, and all those I have fostered and worked with in rescue/rehome have quickly learned that they get what I offer or they get nothing until the next meal, at which time they will be offered the exact same thing with no additions. So far, even the pickiest eaters I have had have given in within three days. Notice I said 'picky'- dogs with legitimate medical issues don't count as picky because they're sick! Healthy dogs can go several days or even a week without eating and have no issues, as they're 'gorge and fast' type eaters (scavengers/hunters), very much unlike our horses!
Now, all that said, if you're happy to cater to your pup and spoil him a bit, there's nothing wrong with it unless he gets to the point where he won't eat a healthy balanced diet at all.