...preferable to a 20 degree drop. There isn't any benefit from dropping temps at night all of the time afaik. The plants will usually grow slower in colder weather. There is a technique used at the end of flowering where temps are lowered to let the plant know that Fall is coming. Plants tend to respond by ripening faster, but this is only done shortly before harvest.
Separate from the air temperature is the radiant heat emitted by the lights. Regardless of whether or not the average air temps inside the grow area lower noticeably at night, the plants still get cooler. This effect usually satisfies any reasons to lower the temps at night manually so you can keep air temp steady 24/7.