From what I can tell it's a 'refinment' of the sear surfaces, but that is a bit of a guess from looking at mine.  IMHO 3lbs is about just right for a hand gun (or rifle).  The main issue is to have a crisp pull.  I have no issue with a 5lb pull as long as there is no creep.  And the stock FA triggers can have some creep.  Also Anything under 2.5lb can start to be a little touchy.