Trim all large fan leaves beginning of week 6. When this is done it transfers all the energy that would go to those leaves to the buds.
I know there are lots of opinions on both sides of this fence. And I've seen plenty anecdotal evidence that would suggest the best results come from extensive defoliation. I've seen just as much anecdotal evidence that it does more harm than good.
The reason I don't trim unless necessary is that I think I should help the plant to mimic what would happen if it were in nature. Many fan leaves do fall off on their own accord (both in nature and in our grow rooms), either late in the season outdoors or soon after our switch to 12/12 indoors. Those that do not fall off (and especially those that are already fully developed) are energy sources not sinks. In other words, if they were no longer providing necessary energy to the plant, they would yellow, necrosis would set in, and the plant would drop the leaves.
So I disagree that cutting fan leaves off increases bud development. My opinion is that the fan leaves continue to provide copious amounts of energy which is then used for all things the plant needs, including bud development. Of course, buds can and usually do continue to develop in size despite the loss of their fan leaves. The plant will be forced to utilize everything else that is green and can photosynthesize. Often the result is the development of additional leaf material (not necessarily fan leaf development) in an attempt to make up for the loss of the plant's largest energy factories. The question is whether or not the observed bud development is larger or smaller than it had the potential of being prior to defoliation. I believe that the observed bud development would have been even more significant had the fan leaves remained.
I'm not saying that trimming should never be done, but my reasons for doing so are usually strategic e.g. to help with light penetration for a bud site that needs additional energy resources.