Although i can see some defoliating is necessary, i don’t recommend too much of it. Air flow can be critical if mold is eminent. But your plants need leaves to make buds.
A couple of things I think are worth mentioning when growers bring up “defoliation”. No amount of nutrients will help the plant grow, unless they are first processed through the leaves. Only then, may mobile nutrients, commonly called "plant food” continues to the buds, for growth. The real name for plant food is called “photosynthate”, but for the purpose and ease of this post, let’s use the term “plant food”.
Leaves" have two main purposes:
1st, You can thank the leaves themselves for 99% of all the uptake of water and nutrients. Plants have a very small chain of water molecules that stretch from root to leaf, within the “xylem” (the woody center part). This ionic chain phenomenon is referred to as cohesion, whereas the entire uptake, from root to leaf, is called “transpiration”. Water is basically the blood of the plant. If you cut any leaves off, you limit the plants resources of water.
2nd, Leaves make all the “plant food” that the plants use to grow, while managing waste (O2), through the stomata. The stomata are very small pore-like openings in the bottom of the leaf, which exchanges new CO2 and O2, and water evaporation. “Plant food” is made through a process called photosynthesis, with in the chloroplast. Leaves are like a big food engine, but instead of 2 fuels like a car (gas & O2), leaves have 3 fuels (CO2 & Nutrients & PAR).
So, why remove them?
I’ve never liked the term of “defoliation” as it means “to strip (a tree, bush, etc.) of leaves”, implying all of them. I prefer to use their relative nick-names, “lollipopping”, “schwazzing” or even “pruning”, to limit confusion. These methods are not something I would promote anyone who desires larger yield, especially outside in full sun or if using auto-flowering seeds. Realistically, removing “any” healthy mature leaf will hinder growth & yield. A good rule of thumb would be to let the plant itself decide naturally what she wants to keep.
Distinguishing the different terms of training, or pruning growth is also a factor. Pruning a branch off the main stem, to manipulate growth direction, is not defoliation. Defoliation includes only leaf matter.
Growth “time span”, is also something that plays a roll. Depending on the cannabis grower’s view, any plant manipulation while in vegetation cycle may not be viewed as playing a role in final yield, while referring to defoliation. As an example, a farmer could prune half the vegetation off in veg cycle, but gives enough time for the vegetation to grow back, before entering into flower. If the factor of “time” itself is removed, the outcome of yield could be viewed differently. This does not apply to Auto Flower strains, as the cycles are fixed, and not based on light cycles.
Understanding what the flower actually is, is also important. Cannabis, being an “incomplete flower”, and a “raceme” type, generally has only male or female parts, where a complete flower has both. Nowhere within the flower itself, is there any leaves. Leave form around each flower. A “Raceme” is a flower cluster with the separate flowers attached by short equal stalks at equal distances along a central stem.
The “flowers” them self, do NOT require any light. No amount of light that’s exposed to each flower will help it grow any measurable amount, or yield more. It the physical features simply aren’t there for any measurable amount of photosynthesis to occur.
In botany, a “bud” is a knob-like growth on a plant that develops into a leaf, flower, or shoot. Only in the cannabis world does it mean “flower clusters”, in a slang fashion. Realistically, referring to a “bud” would be closer to saying “cola” or “meristem”, as it contains flower and leaf, and usually the primary growth area of the shoot.
Where/what is this sink?
“Sinks cells” are areas of new growth with low osmotic pressure. Leaves are areas of high pressure, hence why “plant food” or “photosynthate”, flow from high pressure leaves, to low pressure sinks; commonly called “osmosis”. Sinks can be in the roots or the shoots of the plant (new growth). After the plant food has been manufactured in the leaves, it enters into the phloem, starting at an area in the leaf called “source cells”. From here, osmosis carries “plant food” to its destination and use.
Now for an overall recap. Nutrients use the water to hitchhike a ride, up the xylem, to the chloroplast in the leaf. The leaf processes the raw nutrient into plant food. Then, plant food, enters into the phloem, and high pressure pushes it throughout the plant to areas of low pressure and use.
I do not recommend the removal of any healthy, mature leaf.
Good luck & happy growing