Are foreign keys really necessary in a database design?

Question

As far as I know, foreign keys (FK) are used to aid the programmer to manipulate data in the correct way. Suppose a programmer is actually doing this in the right manner alr

Answer 1

The best thing about foreign key constraints (and constraints in general, really) are that you can rely on them when writing your queries. A lot of queries can become a lot more complicated if you can't rely on the data model holding "true".

In code, we'll generally just get an exception thrown somewhere - but in SQL, we'll generally just get the "wrong" answers.

In theory, SQL Server could use constraints as part of a query plan - but except for check constraints for partitioning, I can't say that I've ever actually witnessed that.