I always post my comments with 'no karma bonus' checked off. Even though I can post at default of +2 I do not do so often. This is because posting at +1 gives a safety margin. You can say more controversial and challenging things in a +1 comment and not have it modded down. But it gets saved in the permanent archive. When I do have something of note to add to the discussion, it gets marked up to +2 or higher fairly quickly anyway.