As Noods said it comes down to personal prefs and beliefs.. but having tried a myriad of possible light/dark regimes, I personally go 24/7 all the way now with autos. Why? Well this is how I see it:
A) You get much better overall control over your environment = more stable growing = better yield / no night/day shifts in temps or humidity
B) Your plants grow faster
C) You get bigger yields because the buds get more light
D) There is well-established science which shows that that not all plant species need a
physical night-cycle, and cannabis is one of them
E) Your pots dry out quicker allowing for more water/nutrients to go into the soil and plant (they use more if there's more light)
F) You see less stretch (not a huge amount less but less)
The downside:
A) It costs more in electricity and wear & tear of your components
B) Although you get more control over environmental stability overall, you lose the chance of having a night period in the warm part of your day and that's really useful for some growers
C) Your plants need more careful monitoring and looking-after
overall because they're working harder 24/7 and using more water & nutes etc.
So, yeah, basically the best answer to give you is to consider the different variables in your own, specific grow room and weigh-up whether you should/could go 24/7 or wotnot.
