I did a run with moderate defoliation. And I did a different run with zero defoliation with a different strain, different set up, different grow medium, different watering method, different nutrients. Ok pretty much everything was different between the 2 runs. BUT....
The difference I noticed between the two runs of defoliation vs zero defoliation has absolutely nothing to do with strain or anything else. The run with zero defoliation, I noticed that all the buds that were completely covered by fan leaves did NOT mature and stayed small and lime green and essentially unripened. Had I removed half the fan leaves from the top of the canopy, all those buds in the middle of the canopy would have ripened up and swollen up as well. I lost a lot of weight by not defoliating. HOWEVER...
The non-defoliated set up was a top feed to waste in 6x6 hugo cubes with drippers, half ass scrog with everything removed under the screen. The plants were grown in a half ass scrog that ended up stretching way too much. Obviously had I managed the scrog correctly, there would have been no "middle canopy". If each cola was about 8 inches, then there wouldnt have been much of an issue. But the colas stretched to 15 inches, and about 1/3 of the colas didnt ripen up or swell to full maturity/trichomes because there was way too much shade. I figured logically thinking, the fan leaves will take all the sun light and disperse it evenly. Same with the nutrients. Well, I was wrong. Wherever the light reached is what ripened. Where ever was shade, did not grow.
So my take away from this is that defoliating definitely can increase yield and overall quality if applied in the correct circumstance. If I were to grow vertically in a crowded environment, then I would heavily defoliate. And growing heavily and crowding your plants is the best way to use the most footprint and vertical space. So if you grow in this fashion then defoliating will definitely help and you would get the most grams per wattage than any other method probably. This is my understanding and opinion on the matter, without the experience to back it up.