On: A Simple Guide to Five Normal Forms in Relational Database Theory

[kingkilr]

Or if you're storing information about them, say their home address, better to have it in one place than two.

[lolipop1 → kingkilr]

No, simply because they are from different domains and by extension from and for different systems. And as such, a natural ID (or arguably a GUID) can also be said to be more fitting to establish that kind of relation.