
The puppy feeding sheet for Abby for her breakfast said, "toast optional." :-) Her breeder kept litters in the kitchen and I don't think she could resist sharing her breakfast with puppies. Very sweet, however, very unnecessary ... as even her breeder recognized.
As long as your dog has no problem with wheat there really is no harm in giving a small piece of toast to a dog, but in terms of nutrional value it's not much use. So for a young puppy if the toast keeps them from eating their regular meal, I would give it a miss.
... when I got my other dog (he was 1-1/2) the morning meal his breeder fed him was 1/2 a wheatabix in milk. So I guess it is pretty common and not far off from Terrier meal and other products sold as "mixers" for dogs. Except the cows milk, of course, which many dogs do not tolerate well.