Good question! And, I'm not sure of the answer :-( Anyway, I pull the leaves between the end of the two week stretch and just before they start to really build flower development in weeks three and four. I would guess that since the plant grows leaves during the first 3/4ths of flower anyway along with building buds that it doesn't affect it. The reason removing small scrub buds from below the light in flower affects the yield is because the small buds are using the same energy as top buds and when you remove the small ones the energy goes to the buds that are left. With leaves, I believe that since it is basically using different parts of the nutrient that is the reason I think it won't affect yield negatively.
Anyone else wanna chime in?