> I have used triggers to keep audit-logs of changes to certain columns in a table
Another good use for triggers is to maintain customer balance..EG: An INSERT, UPDATE or DELETE involving a customer payment (or in the case of banks (deposit or withdrawals) would automatically maintain the balance in the customer master record.
Another scenario is if you want to put a (check) constraint on your table that refers to other rows or tables. You can't actually do that, and need to use a trigger instead.