Nepotism means hiring friends or family. The advantage there is that you start out with a greater level of trust, depending on how long you've known the person. This must be weighed against the disadvantage that there are likely more skilled individuals to be found. When dealing with delicate matters (i.e. when small mistakes cause big problems), reliability becomes more important.
Most people trust their families more than their work acquaintances. Still, the family member must have more than trust, to do a good job in a skilled profession.
Proof? I'm not going to spend the effort to cite data here, since we have no prior relationship.