I tried backing off my light cycle a couple times, one time I got it down to 8/16 (through multiple steps)
In my understanding its just a trick to speed up ripening (at the expense of yield) though I have read some statements recently that if true would lead me to believe that it might encourage more resin production (potentially gaining some quality in exchange for lost yield). I'm not set up to do the kind of side-by-side experiments it would take to verify that one though..
To elaborate, I have recently begun experimenting with phytohormones so I have been doing alot of reading on the subject.
One of the things I have been looking in to is forcing plants to flower under long light cycles (18-24 hours of light a day). What I have been able to gather so far (from the limited papers I have found on the subject) is that THC/resin production may be reduced (13% THC from a plant that might otherwise offer 15%) it would also seem that the total THC production per watt or meter of garden space would be increased (making it a reasonable trade off).
Additionally its not an uncommon practice to give your crop extended periods of darkness before harvest (anywhere from a day to nearly a week in some cases) to encourage resin production..
What I draw from all this is that darkness may have some influence on potency/quality.
From what I read the harshness of light (particularly UVB) might also have an influencing quality.
An interesting experiment would be to run a couple 2ft tables under 250w hps bulbs however add a couple-few 18" UVB lights to one and reduce its light cycle relative to increased power consumption (60 watts for 4) making your new day closer to 9.5-10 hours.
If you record time to maturation, yield (dry weight) and lastly the most heart breaking part how much hash you get from processing the entire harvest of each table. It would provide a few good data points for future speculation and experiments..