When you add the corner brackets to the edges of a roof section, there's 0.25" hanging down to lock onto the building below. The end result is a sort of "table" where the corner brackets become "legs". During the prototype phase I tested it's strength by dumping as many lead minis that I could find on top and found it just held, so I added the levelling support to act as a central column thus ensuring the "table" remains level.

Make sense? Look again at the instructions if you're still confused.

Pages 10 and 11 of the Roof instructions...it says they are part of the modular construction alighnment features...still cant quites see how it works tho

NOW it makes sense You posted as I was checking...lol