An experienced consultant told me he only saw FK used once in the many
banks he knows. He basically said if you don't know how to use FK then
don't use it. His team uses FK during paper design only.
I too worked in several banks. Only relatively inexperienced developers
use FK but I find them inconvenient.
One of the problems is update/delete. FK often blocks you. We all know
some data is wrong but we can't fix them, in real time trading!
Insert? I don't remember but I think you can't insert a dependent table
before inserting all primary tables. Imagine your dependent table
depends on 2 tables, which in turn depend on 3 other tables.
Remember Wall St is all about quick changes and quick fixes (2 different
things). That's why jmx is so popular – no restart required.