I posted this on the other 12/12 thread;

12/12 from seed works very well with most sativas, as a matter of fact it is the only way I would grow sativa. (guess I'm lazy besides being old)
Sativa typically is a equatorial plant, it NORMALLY grows with a 12/12 photoperiod (or pretty close). Keep in mind it is usually very intense light, but it is only for about 12 hours a day.

Now Indicas' present a different deal, and I have not experimented with too many from seed at 12/12. But again think about this; ever start cuttings for just a few days, then banged them into 12/12. Most indicas' do just fine with that, in fact many people grow just like that or maybe a few more days veg. With great results I might add. I believe you get the most from your lights (regardless of type) by growing many small plants as opposed to a few large plants, but that's me.