You can use triggers to do various things:
Define a trigger on the subject table to ensure that the UPDATE, INSERT, MERGE, and
DELETE statements performed to the subject table are propagated to another table.
Use triggers for auditing. For example, you can define a trigger which causes the
INSERT statements in a log table when an employee receives a raise higher than 10%.
Use a trigger to disallow massive UPDATE, INSERT, MERGE, or DELETE during business
hours.
Use a trigger to set a threshold. For example, you can use triggers to set thresholds
for inventory of each item by store, to create a purchase order when the inventory
drops below a threshold, or to change a price if the daily volume does not meet expectations.
Use a trigger to call SQL stored procedures and external stored procedures.