For what it's worth, I've always disliked
Samuel and
Samantha, which means that I'd never even give
Sam a thought.
I do think it's sensible to use a full form - you never know how fashions might change, or whether a mass murderer or country singer might surface with that same nickname and your ln. That's when a
Rick could become
Richard or
Liza could become just about anything without having to mess about with name changes, mns suddenly becoming fns etc. And full names have dignity and solidity and history that nns don't. For marriage, graduation, congratulatory telegrams on one's 100th birthday etc, a bit of dignity is welcome.