Okay...
First of all, a plant is designed to produce more foliage than it needs. In nature, plants have to deal with bugs and animals, and losing leaves is a regular occurrence. They have grown to compensate for this loss of leaf mass by producing more leaves than they need.
Secondly, one large leaf requires more energy to operate than several smaller leaves that use the same area. The surface area of the large leaf demands that the leaf move quantities of water over distances to keep the leaf cool. This takes energy. The leaf also requires more energy because the stem, from leaf to stalk, is longer. In short, is it any surprise that a larger leaf, just like a larger car, needs more energy to do the same job.
Finally, the stress reaction induced when removing leaves impacts branch growth and decreases internodal spacing. In other words, by removing the large fan leaf the plant compensates the loss of mass by increasing the size of the bud sites through hormonal reactions. Plenty of energy is still available, and as these branches increase in size the amount energy they provide towards their own growth increases exponentially, and proportionally, with the replacement and exceeding of the lost leaf mass.
Thus, by removing a larger fan leaf you force the plant to increase the size and frequency of bud sites. This will obviously require an extended rebound period, which can lengthen the vegetative cycle. On the average all leaf mass is replaced with more, more efficient, leaves within 100 hours. The following 100 hours then allow for amazing vigor as all the branches have access to direct light.
What I think is absolutely idiotic is removing bud sites and keeping fan leaves. You can keep the leaf, and remove the bud site (branch), and the theory is that the plant will focus energy on the remaining bud sites. Not entirely inaccurate... but you wind up with a great deal of "lettuce" and few places to grow on. Perhaps there is a place for this method in a straight to flower clone situation where there is no time to develop the lower branches. But for a grower looking to increase their yield then a little extra Vegetative time shouldn't be a big deal when it can increase the size of the plant by 300% in a very short period. We're growing flowers, which need flower sites. We are not growing fan leaves to smoke. The theory on fan leaf energy has had people doing what I consider to be some bass ackwards shit to their plants.
I find defoliation methods work best when combined with other methods like topping/fimming, and Scrog. Top the plant, allow it to rebound. Defoliate the plant. Allow it to rebound. Scrog the well developed branches. Allow it to fill the screen. Flower. It's like an extra 2 weeks but the difference in the end is dramatic.
One thing I am against is defoliating between weeks 2 and 7 of flowering. Your plant is no longer making new leaf mass (not enough to compensate the loss) so removing leaves during this period removes important growth hormones and energy supplies. After week 7 of flowering there is a lot of evidence that defoliation increases finish weight, but there hasn't been a definitive answer on that process yet.
So to recap... Plants are hearty, they replace leaves very quickly, and the assertion that one large leaf is more efficient than the four leaves directly beneath it is wrong. Apply direct light to the leaves beneath the fan leaf and those leaves will increase in size to compensate as well as develop the bud site they are supporting better than the large fan leaf could. The stress reaction during vegetative growth further strengthens the plant.
Fan leaves are best suited to growing a single strong cola. Side branch fan leaves are best at growing a balanced canopy. It is up to the grower to decide which kind of plant will provide them with the best harvests possible given their personal strengths, weaknesses, preferences, and capabilities.
No one should speak against this method until they have tried it for themselves. I didn't get it until I did it. Now I'm doing it, and I'll never not do it. You can make up your own mind. If you're not "baller" enough to have a spare plant off to the side to experiment on then you can hardly call yourself a grower; not of your experience base at the least.