regarding triggers

is there an advantage of using a trigger? when the same job can be performed by a stored procedure?

one more question is as follows:
suppose i have a table x, with a primary attribute 'a'

and i have a table y, with the primary attribute 'b', and a foreign key 'a'.

suppose i say delete from x where a = '1',

it means that not only the rows from x get deleted but also rows from y get deleted.

now i have a trigger which is written for deletes taking place from the table y.

however if i say delete from x where a = '1',

will the trigger (mentioned above) still be called? (because delete are also taking place from the table y)

thanks,
regards
Surabhi