Geometry in Rhino Grasshopper

Hi, I am new to rhino grasshopper. What is the difference between box that you build in rhino and assign it as brep in grasshopper with the box that you make in grasshopper from geometry tab. This is because I make blinds from box in grasshopper in a room that is assigned with brep in grasshopper. When running the diva I have to flatten the object to make the blind works. I also attached the example file. (18.6 KB)
coba v1.3dm (260.2 KB)