There's a lot of skepticism and debate behind this subject. There are many people out there who do this and swear by it. However, a lot of growers here at MarP warn against it. The idea behind it is that every fan leaf absorbs light energy for use in photosynthesis. If you cut the fanleaf off, that's one less leaf for light energy to be stored in, resulting in less energy to be burned in photosynthesis. The flowers of the marijuana plant do not absorb light. Therefore, they do not need to have light hitting them in order to bulk up.
On the other hand, the counter arguement is that by trimming off the fan leaves, you stress the plant into throwing more hormones to heal it, resulting in more growth on your flowering sites. Also, it opens up the canopy to the lower fan leaves, helping your lower flowering sites to grow more densly.
A lot of growers compensate for the lower branches that have popcorn buds from on them by cutting those branches off early into flower. Basically, they trim the bottom 1/4 to 1/3 of the plant. This also "stresses" the plant into "throwing more hormones" to heal those sites, resulting in vigorous bud growth in the early stages of flowering. When doing this, they leave the fan leaves up top to defoliate under their own accord.
Having said all that, my personal experience is that the plant will get rid of the fan leaves that are of no more use to it when it's ready to do so. I trimmed the bottom 1/3 of my plant, and topped and fim'med her numerous times. As you can imagine, at one time, my canopy was very dense with foliage. After a bit of trial and error, the plant's dropped a lot of those leaves, but I still have yet to take any off myself. I've seen the vigorous growth I've read about first hand, and have a hard time justifying not trimming the bottom portion of the plant in the future. I personally would not trim your fan leaves, but rather, the lower branches that aren't receiving enough light. Your ladies will take care of defoliating themselves.
I do not believe and will never believe that cutting off fan leaves makes a plan t produce more hormones that result in more flowers. I have never seen any kind of reliable source advocating this kind of thing. Cutting off the bottom 1/3 of the plant is entirely different and is done to prevent the small popcorn buds that many get on the lower parts of plants and concentrate the growth on the upper part of the plant where the light is more intense.
I dont believe in it niether yual need to look at it like this. Yual put yur plant into flower so it will "flower" right well ifin yual want it to focus its energy on budd production then yual go and start lobbin of limbs the plant going to do what any normal living thing would, its going to stop the bleedin or focus on the wound to heal it. So it will take focus away from budd production and focus on healing its injuries thus being counter productive to what yual wantin the plant to be doin. Leave limbs alone the plant will shed them after she drains the energy from them to feed yur budds.