what are those 3 passwords for ?

I see postgres has 3 password mechanism:

'createuser -d -P arnuld' -- which will ask for the password
according to P flag used here.
'createuser -d -P -W arnuld' -- which will ask for the 2 passwords
belonging to P and W flags.
It does not matter
whether both passwords are same or different.
because it always
creates the user successfuly.

createdb --owner arnuld -W arnuldforum -- one password asked because
of W flag.

Now I want to ask , when you pass the username and password to some
forum software like phpbb3, which password you will pass when you can
pass only one ?

--
http://uttre.wordpress.com/2008/05/14/the-lost-love-of-mine/