Ok so here are my thoughts. First to answer your question, no I haven’t seen any completed and well documented side by side comparison grows that detail defoliation as positive or negative. I believe that you don’t see them because the evidence supports both sides equally. What I mean by that is I think that you could potentially get higher yields by choosing not to defoliate but the quality of the bud will suffer. I also believe that while defoliation can potentially lower yields, the quality of those yields makes up for any loss in weight. I define quality by bud density, trichome production, and size.
During Veg, if you're looking to grow plants fast then I would say defoliation would be detrimental but if you’re looking to methodically train and shape your plant, tactical defoliation can help slow down the growth allowing for more structured and even growth across all branches.
In Flower I don’t think that the benefits of defoliation are based on the bud site’s exposure to light so much as their exposure to wind and space. Being a wind pollinated plant, the buds grow larger and healthier when they are exposed to gentle breezes throughout flowering. Excess leaves only serve to block those breezes thus stunting the development of the buds leaving them smaller and less dense. As with all things in life, finding the right balance is the key to being successful, taking away too many leaves can be detrimental. Defoliation during the early stages of flower can open up space for lower branches to stretch to the top of the canopy while they would have been stifled under heavy foliage. Defoliation late in flower can help to lower humidity to levels that increase trichome production.
These are my experiences with defoliation and I would encourage every grower to have their own experiences. I lollipop and defoliate every one of my plants to achieve the quality of bud that I desire most. I’d rather not spend hours trimming little airy buds that don’t pack quite the same punch as their counterparts higher up on the branch, even if it means losing out on an ounce or so in weight. To me better yields means better quality not increased quantity.