Personal experience with this, I do see that my plants are "shinier" when I give them dark for 48 hours before harvest. More important to me, and I believe it since I read it from Arjan Roskum, is putting them into 48 hours darkness before I flip to 12/12.
Also, I grew two widow grows simultaneously, and I flushed one for 12 days (5 days plain water, 7 days with 1 cup sweet leaf to 25 gal water) and did not flush the other......I dried and cured both the same (5 day hang, 3 days paper bag, 2 weeks canning jars) and I promise you that the flushed weed burned better, didn't crackle and pop, and had a more "marijuana" taste....the un-flushed weed went out alot (I only smoke joints, and an occasional bonger), crackled while burning, and tasted like cat piss & oranges. So, I believe in flushing........just my HO.