Athosanswered grow question 4 years ago Sure, time mainly. A regular photoperiod needs at least 4 weeks before going into flowering, which takes 8 to 10 weeks; so you are looking at 12 to 14 weeks before harvesting. An auto takes 8 to 10 weeks total, so you harvest 4 weeks earlier. That's the main advantage. Another, in places where winter is really cold, the 12 hours of lights out can be detrimental to the health of photoperiods, forcing you to to heat the space, which can be expensive, an auto can as easily run 24/0 using the heat of the lights to keep the grow space warm