As someone who is defoliating several plants right now as an experiment I can clearly see the results.
Large fan leaves are replaced by smaller fan leaves from the lower branches. As fan leaves are removed the plant responds by increasing the size of the leaves on the lower branches. The increase in direct light further develops these branches. Rather than removing lower growth sites, you remove fan leaves, it makes PERFECT sense for those with a brain to use. I'm growing bud sites in veg so that I can grow lots of big nugs in flowering. Seems like too many people are stuck in the mentality that we are growing lettuce. Removing the bud sites to keep fan leaves we'll trim off at harvest and toss anyway... Doesn't make sense like this method does.
By keeping the lower bud sites, developing them early on, I get thicker stems, a fuller canopy, more places to grow nugs, and when the nugs to grow the plant can grow them bigger. Not because the buds are getting light but rather because time and energy were spent early on developing a strong vascular system in those lower branches to support these nugs.
Seems like you guys are growing some skinny ass plants if you think the loss of a couple fan leaves from the main stalk is going to ruin the harvest. I know that I remove one leaf only to find four more beneath it that weren't getting the light they needed. The large fan leaf required more energy to maintain itself; transpiration and the transportation of water and energy from the roots to the leaf. After taking the single large leaf the smaller four leaves, which are more efficient energy producers, will replace the lost leaf mass in under 48 hours by increasing their own sizes. It is really quite amazing how Marijuana responds with this method. I've grown enough of these plants without defoliation to see the difference without a side-by-side comparison.
Besides, can you guys really not afford to just try this out on one plant in your own garden before trying to beat it down? A couple CFL bulbs or a spare corner of the grow room is all you need. Worst case scenario for you people is us being right, which is probably why you're resisting it.
Now, for those that are all, meh I don't trim my other plants... You've probably never grown Roses or Apples before.
http://www.google.com/url?sa=t&source=web&cd=7&sqi=2&ved=0CC0QFjAG&url=http%3A%2F%2Fscholar.lib.vt.edu%2Ftheses%2Favailable%2Fetd-11252002-110834%2Funrestricted%2FETD-2.pdf&rct=j&q=defoliating%20for%20bud&ei=pruoTJO3L4KesQOT5piHDQ&usg=AFQjCNECBjsTWy5b2egDrCi-9mTImqj94g Scroll down to page 5. This is a university study showing the effects of gradual defoliation on fruit production. Your guy's theory against this method is most clearly unfounded, while defoliation itself is still holding ground against the naysayers.
Here's a community of people who have been working this method on a much larger scale. There is a tremendous amount of evidence FOR defoliation here:
http://www.icmag.com/ic/showthread.php?t=174163
@UncleBen: Defoliation is a process best suited to vegetative life, when the plant is actively creating vegetation (leaf mass). During this time a lost leaf is replaced/compensated for quickly by the rest of the plant. Removing a fan leaf after the 2nd week of flowering will not allow the plant to replace this lost mass as it is now focused on producing flowers rather than foliage. During the 2nd to 8th week of flowering I believe that defoliation should be discontinued. During the final weeks of bloom there is some evidence for the removal of most leaves that have long stems to induce a beneficial stress reaction in the plant. I haven't seen this first hand but think that there is ample evidence to encourage further testing.