Is there any value in using trigger conditions rather than function conditions

Hello,

We have elements in our setup that have been around for quite awhile. We are currently running 9.2 and I was wondering
ifthere would be any significant performance increase by moving the conditions out of the function into the trigger...
likewould avoiding the function load save anything.... or would the function be loaded regardless? The function is used
bymany tables to avoid having to explicitly define the timestamp in every query. We have a similar trig/func setup for
recordingthe DB operator at the moment. 

An example trigger:

CREATE TRIGGER update_members_stamp
   BEFORE UPDATE
   ON members
   FOR EACH ROW
   EXECUTE PROCEDURE update_stamp();

The shared function:

CREATE OR REPLACE FUNCTION update_stamp()
   RETURNS trigger AS
$BODY$
BEGIN
-- if the stamp is being manually manipulated, then we will leave it alone
IF NEW.stamp ISNULL
OR NEW.stamp = OLD.stamp
THEN NEW.stamp := NOW();
END IF;
RETURN NEW;
END;$BODY$
   LANGUAGE plpgsql VOLATILE
   COST 1;


If we did something like this would there be any real benefit on a moderately busy table? (ideally I would like to
embedthe action in the trigger but that does not seem possible) 

CREATE TRIGGER update_members_stamp
   BEFORE UPDATE
   ON members
   FOR EACH ROW
WHEN NEW.stamp ISNULL OR NEW.stamp = OLD.stamp
   EXECUTE PROCEDURE update_stamp_x();

CREATE OR REPLACE FUNCTION update_stamp_x()
   RETURNS trigger AS
$BODY$
BEGIN
NEW.stamp := NOW();
END IF;
RETURN NEW;
END;$BODY$
   LANGUAGE plpgsql VOLATILE
   COST 1;