"In the current study we observed substantial compensation in defoliated plants growing at low density, despite losing 75% of leaf area prior to the onset of flowering. Plant responses associated with compensation included (1) increased reproductive efficiency, which may in turn may have resulted from increased canopy light penetration and transient increases in leaf-level photosynthetic rates; (2) greater allocation to reproduction (RA); (3) changes in biomass allocation from roots to shoots; (4) lower leaf longevity, and (5) increased percent fruit set. Although some of these responses were also observed in defoliated plants grown at high density, the inability of high-density plants to compensate appeared to result from competition for light; these plants delayed reproduction and continued to produce new leaves late in the growing season after low-density, defoliated plants had shifted allocation of resources to reproduction."
-- Oecologia July 1997, Volume 111, Issue 2, pp 225-232 Defoliation of the annual herb Abutilon theophrasti: mechanisms underlying reproductive compensation
"Floral development in emerging shoots of unrooted hardwood Chinese gooseberry (Actinidia chinensis Planch.) cuttings was enhanced by continuous defoliation, inhibited by total shading, and unaffected by tipping. Leaf production and growth, shoot elongation and thickening, and new bud development were similarly affected by such treatments. These effects were generally related to severity of treatment and length of time treatments were applied."
-- New Zealand Journal of Agricultural Research Volume 18, Issue 4, 1975. Effect of defoliation, shading, and tipping of shoots on flower bud development and vegetative growth of Chinese gooseberry (Actinidia chinensis Planch.).
"Three experiments were done in an open-sided glasshouse during the normal winter growing season. In experiment 1, swards of the Dwalganup strain which were severely defoliated, either after flower initiation or at early flowering, had 17% more flowers per unit ground area than uncut controls. Swards which were defoliated at both stages had 28% more flowers than the controls."
-- Australian Journal of Agricultural Research 23(3) 427 - 435. The effect of defoliation on flower production in subterranean clover (T. subterraneum L.).
"Swards of three strains of subterranean clover (Seaton Park, Yarloop, Midland B) were subjected to a range of defoliation treatments.
In all strains, cutting at weekly intervals at a height of 1.5–2 cm from 1 month after sowing until the onset of flowering led to a slight delay in flower initiation but the time of flowering was little affected. The rate of inflorescence production, however, was always increased, as was the total number of inflorescences produced by the end of flowering. In particular, seed yields were increased by at least 30% compared with uncut controls."
-- Australian Journal of Agricultural Research 29(4) 789 - 801. The effect of defoliation on inflorescence production, seed yield and hard-seededness in swards of subterranean clover.
"When the external nutrient supply was high, removal of the laminae of fully expanded leaves, which comprised about two-thirds of the total leaf area, did not reduce leaf expansion. When the nutrient status was low, these leaves were of primary importance, presumably because of their role as a source of labile nutrients."
-- Annals of Botany Volume 30 Issue 2 Pp. 173-184. Leaf Growth in Dactylis glomerate following Defoliation.
"Partial defoliation always induced rejuvenation in photosynthetic rate of remaining leaves. Young and middle-aged leaves rejuvenated to rates comparable to those of recently expanded leaves but old leaves only partially rejuvenated. Time after defoliation to attain peak rates increased as leaves aged; values were 5, 9 and 12 days for plants partially defoliated on days 16, 30 and 65 of regrowth respectively. Peak rates were maintained for only 3 or 4 days before declining. Rates of photorespiration and photosynthesis were closely coupled. Transpiration rates varied over time in a similar but more erratic pattern to net photosynthetic rates.
Changes in net photosynthetic rates associated with senescence, defoliation treatments and irradiance levels were largely attributable to changes in intracellular resistance to CO2 transfer. Intracellular resistances ranged from 2.6 to 30 s cm-1, constituting 67-95 % of the total resistance to photosynthesis. Stomatal resistance to CO2 diffusion remained low, 0.2 - 1.0 s cm-1, for all but very old leaves.
Partial defoliation followed by continual removal of new crown and stubble shoots induced very high net photosynthetic rates, c. 15 days later. Highest net photosynthetic rate was 238 ng CO2 cm-2 s-1."
-- Australian Journal of Plant Physiology
1(4) 561 - 578. Influence of Partial Defoliation on Photosynthesis, Photorespiration and Transpiration by Lucerne Leaves of Different Ages.
So it seems to be important which leaves you remove, if you do it correctly you can expect more "above the earth" growth afterwards. Interestingly older Leaves may be able to rejuvenate and take the role of the removed leaves. Nevertheless defoliation seems to slow down the root growth, because assimilates are reallocated to the new growth and not longer to the roots. This retardation lasts for the recovery time, until the plant has re established a new balance. Those are some basic things which will be mostly important in the vegetative state. Additionally it seems to be important how much nutrients are available for the plant to work with. If soil nutrient levels are low, defoliation hits the plant more.
Just some stuff I found. Like I said there isn't much info that is focused on marijuana plants but it is a technique.
A very well developed root structure and a very healthy mature plant seems to be key.
