there are a couple of argument in favor of defoliating during flowering. with many caveats hoewever, and should be done cautiosly.
first of all I would like to say that the argument "leaves are the power cells of plants" etc etc etc is not 100% correct. in indoor conditions, if leaves are not reached by optimal light irradiation they actually take up more sugars than they produce. this means that the more illuminated leaves have to cater for the maintenance of the worst illuminated ones (and thus focus less on growth or bud formation). this said, defoliation in early stages of flowering should be done only in extreme cases of overcrowdness, and mostly with indica strains (they respond better to defoliation and have bigger leaves which cover up each other much more). excess defoliation at the wrong time can severly reduce your plant growth and final yield.
again, this should be done only in
indoor growth, when growth light doesnt have an optimal penetration. outdoor growths have no such issue and dont need defoliation.
the second one (and more imprtant) is that stress signals or damage signals trigger a response in plant. especially the damage signals (which mimicks the damage from herbivores) from removing few leaves trigger an increased production of defence compounds. most defence compounds produced in responce to damage are secondary metabolites. and guess to which category THC and CBDs belong?
same goes to a certain extent when applying stress (like flushing the nutrients away for a week).
both techniques (defoliation and flushing) have the effect of increasing the production of THC and friends in the trichomes. this is hard to prove "at home" however because you cannot measure the THC/CBDs content by yourself (you can get an indication when you smoke it though hehe).
is true on the other hand that these techniques have a definite impact of growth. as such you should never defoliate or flush early in the flowering cycle, but rather towards the end of it, when buds are pretty much formed. and never exxagerate with both.
at a certain point in flowering however plants are not really investing energy into growth anymore, meaning that removing leaves will have little to no impact on bud growth, but will have a positive impact on potency.
in the end you dont really care of making 100g of less potent weed when you make maybe 95g of much more potent one through defoliation or fluching
cheers
Dr Ghard