I experimented with defoliating for my first grow and I thought it worked great. I feel like the day 21 thing can be a little too early for most people though. After watching the three a light defoliation video clip (the one everyone probably seen) I noticed that they defoliate after some pretty good bud growth. On my day 21 of flower my buds didn't look close to the size of theirs in the video at the time of defoliation. So what I did was defoliate the lower half on week 4 (when they got bigger) then defoliate the upper half on week 5. I also did a mild lollipop at the beginning of 12/12.
Here it is day 40
View attachment 950415
And here it is today at day 60
View attachment 950416