The main thing to keep in mind is that the indoor experience is not a replica of outdoors. The strains that are best suited for indoor growth have been bred and grown indoors for generations. Whether you grow in soil or hydro, under fluoros or HID, the only link between the indoor grower and the outdoor grower has to do with plant mechanics. Things like uptake of water and nutes, maturing, sexing. These are basics that exist in both worlds. For that matter, the production of sugars is basically the same in both worlds as well. It's just with the indoor world, we can control many more of the factors than the outdoor farmer. We choose when to go from a vegetative timetable to a flowering one. We decide on ALL the factors of a grow. Humidity, temperature, the works. Let's see an outdoor farmer grow his plants to full maturity in just 4 months.
Having said that, the objective of growing indoors has to be kept in mind when deciding whether to go 24/7 or 18/6. If you are trying to create a little piece of the outdoors indoors, then by all means, have a nighttime. You might want to hook up a high velocity fan and blow your plants over once a season to replicate a wind storm, and if you live in the north, perhaps a blast from a CO2 fire extinguisher would seem like frost. Obviously, that is not the point. The goal is the best, biggest crop in the least amount of time. Taking 6 hours a day in the dark means your plants lose 42 hours of growth each week. Why waste all that time when your plant could be photosynthesizing it's green butt off. Plants don't need REST. That's what is so amazing about them. Give them the right ingredients, and they do the rest.