Some people believe that leaving every leaf on the plant is more beneficial because the leaves are the "solar panels" for the plant so their idea is that leaving them all on lets the plant absorb more light, wven if the leaves are overlapping, apparently. There is some merit to this though as leaving it alone does not stress the plant. At first.
Also, a lot of people against defoliating are against it because they tried it before, did it wrong and removed too many and then complained thay "defoliation ruins your yield". Nope, defoliating did not ruin your yield, you stripping the plant bare did.
Now allow me to explain why i choose to defoliate and how i believe it should be done.... firstly, the principle of defoliation is a a simple one. Leave as many leaves on as you can AS LONG AS they are not blocking a growth tip/node and as long as you have sufficoent airflow through the plant. So first, look down at your canopy from above. If you get to the point where you can see your table/soil/hydroton/floor then you have removed too many. Remember, anywhere that your light is hitting the floor is wasted energy, a space where a leaf could be soaking it up. So use your judgement and get a feel for what the girls want but just focus on 2 main ideas, remove any leaves thatvare blocking growth tips from the light while making sure that you dont remove any that yoi dont need to
You also want to try to oncrease airflow through the plants to decrease the chance of bud rot.