[butlerm]

> If that's the case, you will have an overhead anyway, the only question being whether it's at the DB level or at the application level.

Inserts and updates do not require referential integrity checking if you know that the reference in question is valid in advance. Common cases are references to rows you create in the same transaction or rows you know will not be deleted.

If you actually want to delete something that may be referred to elsewhere then checking is appropriate of course, and in many applications such checking is necessary in advance so you have some idea whether something can be deleted (and if not why not). That type of check may not be race free of course, hence "some idea".