I believe the main concept of light schedule is to re-produce the sun natural light cycle. Growing indoors you can manipulate that light schedule to achieve maximum growth depending on your indoor setup and environment. For example autos can grow under 24/0 light because of genetics mainly the ruderalis strain. Personally I might give them a little more rest if they are undergoing some kind of stress but other than that it's not really necessary. You want them to grow as mush as possible. If your using 12/12 for photoperiods that is pretty much the normal.