When you cut the lights off in flowering state, what usually occurs is flowing of resin. Now what is bad to flowering plants if there is a light leak where it confuses the plants in flower to revert back to vegetative state. When I harvest several plants I usually leave the lights off for 24 hours and there are about 4 flowering plants left that will finish weeks after. Never harmed my flowering plants at all. Just be sure if you do that you have a dehumidifier on 24/7 when the lights are off because the humidity will jack up really high.