I don't think giving nicknames as full names is wrong, persay, but it's definitely not my preference. I myself tend to go by a nickname fairly routinely, but I love having the choice and flexility of using my longer, more formal name. To use your example, a
Samuel can always go by
Sam, but not vice versa.
That said, like several others have mentioned, I (subjectively) feel more strongly about some names than others. Names like
Eliza,
Max, or
Leo can stand entirely on their own, and
Sam is borderline for me.
Sammie, though, would definitely be out.