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

Foreign keys had never been explicit (FOREIGN KEY REFERENCES table(column)) declared in projects (business applications and social networking websites) which I worked on.

But there always was a kind of convention of naming columns which were foreign keys.

It's like with database normalization -- you have to know what are you doing and what are consequence of that (mainly performance).

I am aware of advantages of foreign keys (data integrity, index for foreign key column, tools aware of database schema), but also I am afraid of using foreign keys as general rule.

Also various database engines could serve foreign keys in a different way, which could lead to subtle bugs during migration.

Removing all orders and invoices of deleted client with ON DELETE CASCADE is the perfect example of nice looking, but wrong designed, database schema.