12/12 from seed is forcing the plant to switch to flowering sooner. It has a purpose ffor those who just don't have the time to allow a full veg but there is a cost. It still takes time for the plant to grow enough to be able to produce and support fflowers but it is also quicker than standard. the problem is that MJ needs the opportunity to mature in order to produce at its optimum level. If it is forced to flower before it is naturally ready, it will not have the ability to produce the quality or quantity of buds that it is genetically predetermined to have.
It is certainly possible to fflower straight from germination. But I can't see the payoff being any better than just buying and running autos.