Typically, I don't like using nns that end in the "ie" sound as full names.
Molly,
Maisie, etc just sound so cutesy to me. Names that end in A, on the other hand, are fine (like
Lisa).
Boy names are a little more complicated. Many nns, like
Tom and
Jim, sound too inconsequential to be full names.
Jack, on the other hand, sounds fine to me.