I read a thread about defoliation a few years back. It completely changed my style of growing but more importantly it increased my yield by a
huge margin. I'll explain my process and timing as it is vital to increasing yield and limiting stretch.
First lets determine what leaves should go when you defoliate. I will pluck any fan leaf from a node that has a developed off shoot. If the leaves on that side branch are at least a half inch long your fan leaf can go. Just make sure you're young offshoot looks like a very small but developed 3 leaf.
During the entire stage of vegetation I pluck every fan leaf when it's time. I also tie down my plants to keep an even canopy. Defoliation and tying your plants down is a great combination to ensure all your side branch leaves get maximum light and air flow.
I stop all defoliation 3 days before I plan on switching my lights to 12 / 12. At this time I make sure to defoliate EVERYTHING below the canopy line side branches included! During the first 2 weeks I will weave them into my netting as they stretch. On the 15th day I will cull every single fan leaf that has developed side clusters. When you are finished they look VERY naked.
At day 30 they will look bushier than ever with almost no light making through the canopy. I once again complete a culling of new fan leaves that have developed nodes. They will look naked once again but this time with pretty decently developed flowers.
At day 45 I do my final cull of fan leaves, and then let them do their thing until they are completely finished out.
I have noticed a few things using this technique over the years. Doing a cull all at once is better than daily plucking during flowering. I have used both methods and prefer the culling method. The plants snap back pretty quickly and are not under the constant stress of loosing leaves daily.
When you are fertilizing your plants don't hold back. Go with your usual dosage even after you strip more than half the leaf matter from your plants.
In the wild a fan leaf is a pretty necessary thing. Not only is it a solar panel but it is also a holding center for the plants nutrients. Indoor grows where you control a constant supply of food to your plants makes the fan leaf less necessary. Yes, they are a solar panel but they are also a huge blocker of light to your off shoots which need daily development to achieve greatness.
Culling leaves during veg will create a much more compact plant with much less space between nodes. When you cull during flowering it will help control your plants stretch. Helping you have a more compact and level canopy.
I have included a couple photo's of one of my two flowering girls under an XML 350. She is grown in a 10 gallon air pot with a mixture of Fox Farms Ocean Forest and Humboldt. Each plant should yield at least 8 ozs by week 9. That is double what I used to get before I changed my grow style to include defoliation. Currently she is at day 30 of flowering. I will defoliate her tonight and post pics of the aftermath.