While the plant is alive, it breathes through the stomata, in the leaves.
But right after it dies the stomata close forever, there is no more respiration and transpiration through the leaves.
Keeping the leaves (at least the big shade leaves that won't be smoked) in the plant after it dies just helps trap water inside and slows down the drying.
But you want the plant to dry (not too fast though), so cut them off. At least the big shade leaves.
p.s. there are some places in the world like Morocco or Mexico where the shade leaves aren't always clipped right after harvest. There are some reasons for it:
1- they are dealing with a harvest of tons of weed, and the work is all done by just a handful of people. There are some more important tasks for them.
2- the plants are stacked on the ground til waist height inside dirty shit sheds or even in the open, and keeping the shade leaves on somewhat prevents the buds from getting full of dirt or receiving the bad effects of a midday sun.
3- these people don't really care about the quality of the end product. It's gonna be low grade hash or ammonia smelling brick weed anyway. Why bother?