[wiz21]

GB of RAM is fine until your database is one terabyte.

Also, RDBMS do constraint enforcement for you and that's absolutely critical when you work with any sufficiently big database (I work on a 100GB DB with a team of 6 people, changing here and there and I can't tell you how crucial the constraints are to maintain the data quality in face of bugs, misjudgment, etc.). And no, it's not for lack of testing. When you work on millions of super complex records, you always miss some corner cases (unless you're NASA and have a huge budget to test thoroughly)