It completely breaks immersion I think. And it's so arbitrary.
In real life there are no "levels". Levels should simply be "behind the scenes" aggregates of (perhaps hidden) skills and attributes. In real life you have skills (like swordfighting) and you have attributes (like strength) but there is no equivalent of a level. It should be that way in the game too, levels if they exist should just be calculated on the fly from attributes and skills. And attributes and skills should automatically increase depending on what you do.
Basically I really like the way the nGCD mod handles leveling. It feels very natural.
I'm guessing it means what I tried to describe above.
So of course I voted for Automatic.