SQL: Using NULL values vs. default values

Question

What are the pros and cons of using NULL values in SQL as opposed to default values?

Answer 1

As one responder already said, NULL is not a value.

Be very ware of anything proclaimed by anyone who speaks of "the NULL value" as if it were a value.

NULL is not equal to itself. x=y yields false if both x and y are NULL. x=y yields true if both x and y are the default value.

There are almost endless consequences to this seemingly very simple difference. And most of those consequences are booby traps that bite you real bad.