compileman. Triggers are objects you create that 'fire' (activate) when a row on a table that it was create for is changed (Insert, Update, Delete). It could be for any column or specific column(s). For example:
Table with columns, Price, Discount, Discount Price.
If a trigger is created for Update of Discount, when Discount is Updated, you could have it update Discount Price with Price * Discount.
(This may not be a realistic example as you probably would save a value you could calculate in the table).
Create Insert, Update and Create triggers so that if any column changes, you can Insert the row Before and/or After the change along with the User, and Timestamp to create an Audit table that tracks changes.
As for Stored Procedures, they are basically Programs. As such they can do just about anything you like.
Procedures are part of your database's Somatic nervous system. They fire only when specifically requested.
Triggers are part or your database's Autonomic nervous system. They operate in the background all the time, without concious control.
If it's not practically useful, then it's practically useless.