Some say theres scientific data to back it up that this does add girth to the already existing trichomes.
Yet this "scientific data" is elusive and can never be found. I found that 99% of folks that use the word "scientific data" are using so called science from some guy who writes on a pot-forum or just made it up them selves altogether.
I don't know if THC is only made at night (more "science"), but I have seen auto-flowering plants with no dark period being grown on some wild journals. Lots of BS to wade through.
I have tried harvesting with a dark period of three days and it did little to improve anything (other then to make me wait for three more days). If I don't flush (with room temp RO water) my weed does not taste as good. My wife won't smoke my unflushed bud.
The question is, who is right? I am pretty sure the folks going at it on this thread are growing some quality weed (regardless of side taken). Perhaps both methods have some merit. The answer: Have an open mind and give the different methods a try, then see how it effects your harvest. It only matter if this is your first and last harvest.