"trimming" leaves is one of those age old contreversies that has been debated and discussed time and again. My personal opinion, is "don't". Leaves are the 'solar power supply' for plant growth.
"Photosynthesis is an important biochemical process in which plants, algae, some bacteria, and some protists convert the energy of sunlight to chemical energy. " http://en.wikipedia.org/wiki/Photosynthesis
By week six a lot of the fan leaves should be yellowing withering dieing and falling off by themselves, when they're no longer needed.
One things leaves do is store up nutrients during veg and then uses them during flowering. If you remove these food storehouses you will harm the plant.
At week six you're almost ready for the flush.
I took a lot of my leaves off for many harvests because that was the way I was taught. I took less last time and didn't see much difference, this time I took only yellowing, sickly ones from the bottom. I have noticed that the last two week "push" has been more substantial, they're putting on some great weight. I have noticed (with Sweet-tooth) that it is taking a little longer to ripen. I figure it's because more leaves equal more energy for the plant to use up?