There was a study done on this by a university in the Netherlands I believe, but I'll be damned if I can find it again. Anyways after reading advice from a bunch of stoners I read the study. It convinced me that it works so I tried it. There was a noticeable diff in sugar on em.
Now I have done this numerous times and have not produced consistent results. Sometimes It seems to really help sometimes not so much. I cannot explain why with certainty. The only thing I can come up with is that I may not have had my conditions right prior to the dark. IE. Nutes, ph etc. I did unknowingly have a faulty ph meter at the time. Which was causing me lots of other probs. Sadly I do not have the space to do a dark batch at the moment or I would deff. be doin it again.
One recommendation I would make if you decide to do it is make sure you keep plenty of air mvmt. on em so as to prevent any mold. when I did it I did not water them while in dark either. They were in 5" pots/hydroton Sog style. And did not show any signs of wilt.
The basic theory behind the practice is sound tho. Plants produce resins at night as a natural sunscreen. Throughout the day some of the glands deteriorate only to be replaced the next night. So given up to 72 hrs of dark straight, resin production is allowed to accumulate without deterioration. Leaving more on the plant for you to enjoy.
Don't take my word for it tho. Or the word of a bunch of biased potheads who did it once and did not "see" any diff. Try to find that report(i'm still looking too) I know there is a thread on here with a link to it. Do a test run for yourself and make your own decision.
peace